(a). Introduction to Maps
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Introduction
A map can
be simply defined as a graphic representation of the real
world. This representation is always an abstraction of reality.
Because of the infinite nature of our Universe it is impossible
to capture all of the complexity found in the real world.
For example, topographic maps abstract the three-dimensional
real world at a reduced scale on a two-dimensional plane
of paper.
Maps are used to display both cultural and
physical features of the environment. Standard topographic
maps show a variety of information including roads,
land-use classification, elevation, rivers and other water
bodies, political boundaries, and the identification of houses
and other types of buildings. Some maps are created with
very specific goals in mind. Figure 2a-1 displays
a weather
map showing the location of low and high
pressure centers and fronts over
most of North America. The intended purpose of this map is
considerably more specialized than a topographic map.
| Figure 2a-1: The
following specialized weather map displays the surface
location of pressure centers and fronts for Saturday,
November 27, 1999 over a portion of North America. |
The art of map construction is called cartography.
People who work in this field of knowledge are called cartographers.
The construction and use of maps has a long history. Some
academics believe that the earliest maps date back to the
fifth or sixth century BC. Even in these early maps, the
main goal of this tool was to communicate information. Early
maps were quite subjective in their presentation of spatial
information. Maps became more objective with the dawn of
Western science. The application of scientific
method into cartography made maps more ordered and
accurate. Today, the art of map making is quite a sophisticated
science employing methods from cartography, engineering,
computer science, mathematics, and psychology.
Cartographers classify maps into two broad
categories: reference
maps and thematic
maps. Reference maps normally show natural and human-made
objects from the geographical environment with an emphasis
on location. Examples of general reference maps include maps
found in atlases and topographic maps. Thematic maps are
used to display the geographical distribution of one phenomenon
or the spatial associations that occur between a number of
phenomena.
Map Projection
The shape of the Earth's surface can be described
as an ellipsoid. An ellipsoid is a three-dimensional shape
that departs slightly from a purely spherical form. The Earth
takes this form because rotation causes
the region near the equator to bulge outward to space. The
angular motion caused by the Earth spinning on its axis also
forces the polar regions on the globe to be somewhat flattened.
Representing the true shape of the Earth's
surface on a map creates some problems, especially when this
depiction is illustrated on a two-dimensional surface. To
overcome these problems, cartographers have developed a number
of standardized transformation processes for the creation
of two-dimensional maps. All of these transformation processes
create some type of distortion artifact. The nature of this
distortion is related to how the transformation process modifies
specific geographic properties of the map. Some of the geographic
properties affected by projection distortion include: distance;
area; straight line direction between points on the Earth;
and the bearing of cardinal points from locations on our
planet.
The illustrations below show some of the common map
projections used today. The first two-dimensional
projection shows the Earth's surface as viewed from space
( Figure 2a-2). This orthographic projection distorts
distance, shape, and the size of areas. Another serious
limitation of this projection is that only a portion
of the Earth's surface can be viewed at any one time.
The second illustration displays a Mercator
projection of the Earth ( Figure 2a-3).
On a Mercator projection, the north-south scale increases
from the equator at the same rate as the corresponding
east-west scale. As a result of this feature, angles
drawn on this type of map are correct. Distortion on
a Mercator map increases at an increasing rate as one
moves toward higher latitudes. Mercator maps are used
in navigation because a line drawn between two points
of the Earth has true direction. However, this line may
not represent the shortest distance between these points.
| Figure 2a-2: Earth
as observed from a vantage point in space. This orthographic
projection of the Earth's surface creates a two-dimensional
representation of a three-dimensional surface. The orthographic
projection distorts distance, shape, and the size of
areas. |
| Figure 2a-3: Mercator
map projection. The Mercator projection is one of the
most common systems in use today. It was specifically
designed for nautical navigation. |
The Gall-Peters
projection was developed to correct some of the
distortion found in the Mercator system ( Figure 2a-4).
The Mercator projection causes area to be gradually distorted
from the equator to the poles. This distortion makes
middle and high latitude countries to be bigger than
they are in reality. The Gall-Peters projection corrects
this distortion making the area occupied by the world's
nations more comparable.
| Figure 2a-4: Gall-Peters
projection. The Gall-Peters
projection corrects the distortion of area common in
Mercator maps. As a result, it removes the bias in Mercator
maps that draws low latitude countries as being smaller
than nations in middle and high latitudes. This projection
has been officially adopted by a number of United Nations
organizations. |
The Miller
Cylindrical projection is another common
two-dimensional map used to represent the entire Earth
in a rectangular area ( Figure 2a-5). In this project,
the Earth is mathematically projected onto a cylinder
tangent at the equator. This projection in then unrolled
to produce a flat two-dimensional representation of the
Earth's surface. This projection reduces some of the
scale exaggeration present in the Mercator map. However,
the Miller Cylindrical projection describes shapes and
areas with considerable distortion and directions are
true only along the equator.
| Figure 2a-5: The
Miller Cylindrical projection. |
Figure 2a-6 displays the Robinson
projection. This projection was developed to
show the entire Earth with less distortion of area. However,
this feature requires a tradeoff in terms of inaccurate
map direction and distance.
| Figure 2a-6: Robinson's
projection. This projection is common in maps that require
somewhat accurate representation of area. This map projection
was originally developed for Rand McNally and Company
in 1961. |
The Mollweide
projection improves on the Robinson projection
and has less area distortion ( Figure 2a-7). The
final projection presented presents areas on a map that
are proportional to the same areas on the actual surface
of the Earth ( Figure 2a-8). However, this Sinusoidal
Equal-Area projection suffers from distance,
shape, and direction distortions.
| Figure 2a-7: Mollweide
projection. On this projection the only parallels (line
of latitude) drawn of true length are 40° 40' North
and South. From the equator to 40° 40' North and
South the east-west scale is illustrated too small. From
the poles to 40° 40' North and South the east-west
scale is illustrated too large. |
| Figure 2a-8: Sinusoidal
Equal-Area projection. |
Map Scale
Maps are rarely drawn at the same scale as
the real world. Most maps are made at a scale that is much
smaller than the area of the actual surface being depicted.
The amount of reduction that has taken place is normally
identified somewhere on the map. This measurement is commonly
referred to as the map
scale. Conceptually, we can think of map scale as
the ratio between the distance between any two points on
the map compared to the actual ground distance represented.
This concept can also be expressed mathematically as:
On most maps, the map scale is represented
by a simple fraction or ratio. This type of description of
a map's scale is called a representative
fraction. For example, a map where
one unit (centimeter, meter, inch, kilometer, etc.) on the
illustration represents 1,000,000 of these same units on
the actual surface of the Earth would have a representative
fraction of 1/1,000,000 (fraction) or 1:1,000,000 (ratio).
Of these mathematical representations of scale, the ratio
form is most commonly found on maps.
Scale can also be described on a map by a verbal
statement. For example, 1:1,000,000 could
be verbally described as "1 centimeter on the map
equals 10 kilometers on the Earth's surface" or "1
inch represents approximately 16 miles".
Most maps also use graphic
scale to describe the distance
relationships between the map and the real world.
In a graphic scale, an illustration is used to depict
distances on the map in common units of measurement
( Figure 2a-9). Graphic scales are quite useful
because they can be used to measure distances on
a map quickly.
| Figure 2a-9: The
following graphic scale was drawn for map with a scale
of 1:250,000. In the illustration distances in miles
and kilometers are graphically shown. |
Maps are often described, in a relative sense,
as being either small scale or large scale. Figure 2a-10 helps
to explain this concept. In Figure 2a-10, we have
maps representing an area of the world at scales of 1:100,000,
1:50,000, and 1:25,000. Of this group, the map drawn at 1:100,000
has the smallest scale relative to the other two maps. The
map with the largest scale is map C which is drawn at a scale
of 1:25,000.
| Figure
2a-10: The
following three illustrations describe the relationship
between map scale and the size of the ground area shown
at three different map scales. The map on the far left
has the smallest scale, while the map on the far right
has the largest scale. Note what happens to the amount
of area represented on the maps when the scale is changed.
A doubling of the scale (1:100,000 to 1:50,000 and 1:50,000
to 1:25,000) causes the area shown on the map to be reduced
to 25% or one-quarter. |
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(b). Location, Distance, and Direction on Maps
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Location on Maps
Most maps allow
us to specify the location of points on the Earth's surface
using a coordinate system. For a two-dimensional map, this
coordinate system can use simple geometric relationships
between the perpendicular axes on a grid system to define
spatial location. Figure 2b-1 illustrates how the
location of a point can be defined on a coordinate system.
| Figure 2b-1: A
grid coordinate system defines the location of points
from the distance traveled along two perpendicular axes
from some stated origin. In the example above, the two
axes are labeled X and Y. The origin is located in the
lower left hand corner. Unit distance traveled along
each axis from the origin is
shown. In this coordinate system, the value associated
with the X-axis is given first, following by the value
assigned from the Y-axis. The location represented by
the star has the coordinates 7 (X-axis), 4 (Y-axis). |
Geographical Coordinate System
The geographical
coordinate system measures location from only
two values, despite the fact that the locations are described
for a three-dimensional surface. The two values used
to define location are both measured relative to the polar
axis of the Earth. The two measures used in the
geographic coordinate system are called latitude and longitude.
| Figure
2b-2: Lines
of latitude or parallels are
drawn parallel to the equator (shown in red)
as circles that span the Earth's surface. These parallels
are measure in degrees (°). There are 90 angular
degrees of latitude from the equator to each of the poles.
The equator has an assigned value of 0°. Measurements
of latitude are also defined as being either north
or south of equator to distinguish the hemisphere of
their
location. Lines of longitude or meridians are
circular arcs that meet at the poles. There are 180° of
longitude either side of a starting meridian which
is known the Prime
Meridian. The Prime Meridian has a designated
value of 0°. Measurements of longitude are also
defined as being either west or east of the Prime Meridian. |
Latitude measures
the north-south position of locations on the Earth's surface
relative to a point found at the center of the Earth ( Figure
2b-2). This central point is also located on the Earth's
rotational or polar
axis. The equator is the starting point for the measurement
of latitude. The equator has a value of zero degrees. A line
of latitude or parallel of
30° North has an angle that is 30° north of the plane
represented by the equator ( Figure 2b-3). The maximum
value that latitude can attain is either 90° North or
South. These lines of latitude run parallel to the rotational
axis of the Earth.
Longitude measures
the west-east position of locations on the Earth's surface
relative to a circular arc called the Prime
Meridian ( Figure 2b-2). The position of the
Prime Meridian was determined by international agreement
to be in-line with the location of the former astronomical
observatory at Greenwich, England. Because the Earth's circumference
is similar to circle, it was decided to measure longitude
in degrees. The number of degrees found in a circle is 360.
The Prime Meridian has a value of zero degrees. A line of
longitude or meridian of
45° West has an angle that is 45° west of the plane
represented by the Prime Meridian ( Figure 2b-3). The
maximum value that a meridian of
longitude can have is 180° which is the distance halfway
around a circle. This meridian is called the International
Date Line. Designations of west and east are used
to distinguish where a location is found relative to the
Prime Meridian. For example, all of the locations in North
America have a longitude that is designated west.
Universal Transverse Mercator System (UTM)
Another commonly used method to describe location
on the Earth is the Universal
Transverse Mercator ( UTM) grid
system. This rectangular coordinate
system is metric, incorporating the meter as its
basic unit of measurement. UTM also
uses the Transverse Mercator projection system to model the
Earth's spherical surface onto a two-dimensional plane. The UTM system
divides the world's surface into 60 - six degree longitude
wide zones that run north-south ( Figure 2b-5). These
zones start at the International Date Line and are successively
numbered in an eastward direction ( Figure 2b-5). Each
zone stretches from 84° North to 80° South ( Figure
2b-4). In the center of each of these zones is a central
meridian. Location is measured in these zones from a false
origin which is determined relative to the intersection
of the equator and the central meridian for each zone. For
locations in the Northern Hemisphere, the false origin is
500,000 meters west of the central meridian on the equator.
Coordinate measurements of location in the Northern Hemisphere
using the UTM system
are made relative to this point in meters in eastings (longitudinal
distance) and northings (latitudinal
distance). The point defined by the intersection of 50° North
and 9° West would have a UTM coordinate
of Zone 29, 500000 meters
east (E), 5538630 meters north (N) (see Figures 2b-4 and 2b-5).
In the Southern Hemisphere, the origin is 10,000,000 meters
south and 500,000 meters west of the equator and central
meridian, respectively. The location found at 50° South
and 9° West would have a UTM coordinate
of Zone 29, 500000 meters
E, 4461369 meters N (remember that northing in the Southern
Hemisphere is measured from 10,000,000 meters south of the
equator - see Figures 2b-4 and 2b-5).
| Figure
2b-4: The
following illustration describes the characteristics
of the UTM zone "29" found
between 12 to 6° West longitude. Note that the
zone has been split into two halves. The half on the
left
represents the area found in the Northern Hemisphere.
The Southern Hemisphere is located on the right. The
blue line represents the central meridian for this
zone. Locations measurements for this zone are calculated
relative
to a false origin. In the Northern Hemisphere, this
origin is located 500,000 meters west of the equator.
The Southern
Hemisphere UTM measurements
are determined relative to a origin located at 10,000,000
meters south and 500,000 meters west of the equator and
central meridian, respectively. |
The UTM system has been modified
to make measurements less confusing. In this modification,
the six degree wide
zones are divided into smaller pieces or quadrilaterals that
are eight degrees of latitude tall. Each of these rows is
labeled, starting at 80° South, with the letters C to
X consecutively with I and O being omitted (Figure 2b-5).
The last row X differs from the other rows and extends from
72 to 84° North latitude (twelve degrees tall). Each
of the quadrilaterals or grid zones are identified by their
number/letter designation. In total, 1200 quadrilaterals
are defined in the UTM system.
The quadrilateral system allows
us to further define location using the UTM system.
For the location 50° North and 9° West, the UTM coordinate
can now be expressed as Grid Zone 29U,
500000 meters E, 5538630 meters N.
| Figure
2b-5: The UTM system
also uses a grid system to break the Earth up into
1200 quadrilaterals. To keep the illustration manageable,
most of these zones have been excluded. Designation
of
each quadrilaterals is accomplished with a number-letter
system. Along the horizontal bottom, the six degree
longitude wide zones are numbered, starting at 180° West longitude,
from 1 to 60. The twenty vertical rows are assigned letters
C to X with I and O excluded. The letter, C, begins at
80° South latitude. Note that the rows are 8 degrees
of latitude wide, except for the last row X which is
12 degrees wide. According to the reference system,
the bright green quadrilateral has the grid reference 29V (note
that in this system west-east coordinate is given first,
followed by the south-north coordinate). This grid
zone is found between 56 and 64° North latitude and 6
and 12° West longitude. |
Each UTM quadrilateral
is further subdivided into a number of 100,000 by 100,000
meter zones. These subdivisions are coded by a system of
letter combinations where the same two-letter combination
is not repeated within 18 degrees of latitude and longitude.
Within each of the 100,000 meter squares one can specify
location to one-meter accuracy using a 5 digit eastings and
northings reference system.
The UTM grid
system is displayed on all United
States Geological Survey (USGS)
and National Topographic Series (NTS) of
Canada maps. On
USGS 7.5-minute quadrangle maps (1:24,000 scale), 15-minute
quadrangle maps (1:50,000, 1:62,500, and standard-edition
1:63,360 scales), and Canadian 1:50,000 maps the UTM grid
lines are drawn at intervals of 1,000 meters, and are shown
either with blue ticks at the edge of the map or by full
blue grid lines. On USGS maps at 1:100,000 and 1:250,000
scale and Canadian 1:250,000 scale maps a full UTM grid
is shown at intervals of 10,000 meters. Figure 2b-6 describes
how the UTM grid system
can be used to determine location on a 1:50,000 National
Topographic Series of Canada map.
| Figure
2b-6: The
top left hand corner the "Tofino" 1:50,000 National
Topographic Series of Canada map is shown
above. The blue lines and associated numbers on the map
margin are used to determine location by way of the UTM grid
system. Abbreviated UTM 1,000-meter
values or principle digits are
shown by numbers on the map margin that vary from 0 to
100 (100 is actually given the value 00). In each of
the corners of the map, two of the principle digits are
expressed in their full UTM coordinate
form. On the image we can see 283000 m E. and 5458000
m N. The red dot is
found in the center of the grid defined by principle
numbers 85 to 86 easting and 57 to 58 northing. A more
complete UTM grid
reference for this location would be 285500 m E. and
5457500 m N. Information found on the map margin also
tells us (not shown) that the area displayed is in Grid
Zone 10U and the
100,000 m squares BK and CK are
located on this map. |
Distance on Maps
In section 2a,
w e have learned that depicting the Earth's three-dimensional
surface on a two-dimensional map creates a number of distortions
that involve distance, area, and direction. It is possible
to create maps that are somewhat equidistance. However, even
these types of maps have some form of distance distortion.
Equidistance maps can only control distortion along either
lines of latitude or
lines of longitude.
Distance is often correct on equidistance maps only in the
direction of latitude.
On a map that has a large scale, 1:125,000
or larger, distance distortion is usually insignificant.
An example of a large-scale map is a standard topographic
map. On these maps measuring straight line distance is simple.
Distance is first measured on the map using a ruler. This
measurement is then converted into a real world distance
using the map's scale. For example, if we measured a distance
of 10 centimeters on a map that had a scale of 1:10,000,
we would multiply 10 (distance) by 10,000 (scale). Thus,
the actual distance in the real world would be 100,000 centimeters.
Measuring distance along map features that
are not straight is a little more difficult. One technique
that can be employed for this task is to use a number of
straight-line segments. The accuracy of this method is dependent
on the number of straight-line segments used ( Figure 2b-7).
Another method for measuring curvilinear map distances is
to use a mechanical device called an opisometer.
This device uses a small rotating wheel that records the
distance traveled. The recorded distance is measured by this
device either in centimeters or inches.
| Figure
2b-7: Measurement
of distance on a map feature using straight-line segments. |
Direction on Maps
Like distance, direction is difficult to measure
on maps because of the distortion produced by projection
systems. However, this distortion is quite small on maps
with scales larger than 1:125,000. Direction is usually measured
relative to the location of North or South
Pole. Directions determined from these locations
are said to be relative to True
North or True
South. The magnetic poles can also be used to measure
direction. However, these points on the Earth are located
in spatially different spots from the geographic North and
South Pole. The North
Magnetic Pole is located at 78.3° North, 104.0° West
near Ellef Ringnes Island, Canada. In the Southern Hemisphere,
the South
Magnetic Pole is located in Commonwealth Day, Antarctica
and has a geographical location of 65° South, 139° East.
The magnetic poles are also not fixed overtime and shift
their spatial position overtime.
Topographic maps normally have a declination
diagram drawn on them ( Figure 2b-8). On Northern Hemisphere
maps, declination diagrams describe the angular difference
between Magnetic North and True North. On the map, the angle
of True North is parallel to the depicted lines of longitude.
Declination diagrams also show the direction of Grid
North. Grid North is an angle that is parallel to
the easting lines
found on the Universal
Transverse Mercator ( UTM) grid
system ( Figure 2b-8).
| Figure
2b-8: This
declination diagram describes the angular difference
between Grid, True, and Magnetic North. This illustration
also shows how angles are measured relative grid, true,
and magnetic azimuth. |
In the field, the direction of features is
often determined by a magnetic compass which measures angles
relative to Magnetic North. Using the declination diagram
found on a map, individuals can convert their field measures
of magnetic direction into directions that are relative to
either Grid or True North. Compass directions can be described
by using either the azimuth system
or the bearing system.
The azimuth system calculates direction in degrees of a full
circle. A full circle has 360 degrees ( Figure 2b-9).
In the azimuth system, north has a direction of either the
0 or 360°. East and west have an azimuth of 90° and
270°, respectively. Due south has an azimuth of 180°.
| Figure
2b-9: Azimuth system
for measuring direction is based on the 360 degrees found
in a full circle. The illustration shows the angles associated
with the major cardinal points of the compass. Note that
angles are determined clockwise from north. |
The bearing system divides direction into four
quadrants of 90 degrees. In this system, north and south
are the dominant directions. Measurements are determined
in degrees from one of these directions. The measurement
of two angles based on this system are described in Figure
2b-10.
| Figure
2b-10: The bearing system
uses four quadrants of 90 degrees to measure direction.
The illustration shows two direction measurements. These
measurements are made relative to either north or south.
North and south are given the measurement 0 degrees.
East and west have a value of 90 degrees. The first measurement
(green) is found
in the north - east quadrant. As a result, its measurement
is north 75 degrees to the east or N75°E. The first
measurement (orange)
is found in the south - west quadrant. Its measurement
is south 15 degrees to the west or S15°W. |
Global Positioning Systems
Determination of location in field conditions
was once a difficult task. In most cases, it required the
use of a topographic map and landscape features to estimate
location. However, technology has now made this task very
simple. Global
Positioning Systems ( GPS)
can calculate one's location to an accuracy of about 30-meters
( Figure 2b-11). These systems consist of two parts:
a GPS receiver and a network of many satellites. Radio transmissions
from the satellites are broadcasted continually. The GPS
receiver picks up these broadcasts and through triangulation
calculates the altitude and spatial position of the receiving
unit. A minimum of three satellite is required for triangulation. 
| Figure
2b-11: Handheld Global
Positioning Systems (GPS).
GPS receivers can determine latitude, longitude,
and elevation anywhere on or above the Earth's surface
from signals transmitted by a number of satellites.
These units can also be used to determine direction,
distance traveled, and determine routes of travel
in field situations. |
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(c). Map Location and Time Zones
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Before the late nineteenth
century, time keeping was essentially a local phenomenon.
Each town
would set their clocks according to the motions of the
Sun. Noon was defined as the time when the Sun
reached its maximum altitude above the horizon. Cities
and towns would assign a clockmaker to calibrate a town
clock to these solar motions. This town clock would then
represent "official" time and the citizens would set
their watches and clocks accordingly.
The later half of the nineteenth century
was time of increased movement of humans. In the United
States and Canada, large numbers of people were moving
west and settlements in these areas began expanding rapidly.
To support these new settlements, railroads moved people
and resources between the various cities and towns. However,
because of the nature of how local time was kept, the
railroads experience major problems in constructing timetables
for the various stops. Timetables could only become more
efficient if the towns and cities adopted some type of
standard method of keeping time.
In 1878, Canadian Sir Sanford Fleming suggested
a system of worldwide time zones that would simplify
the keeping of time across the Earth. Fleming proposed
that the globe be divided into 24 time zones, each 15
degrees of longitude in width. Since the world rotates
once every 24 hours on its axis and there are 360 degrees
of longitude, each hour of Earth rotation represents
15 degrees of longitude.
Railroad companies in Canada and the United
States began using Fleming's time zones in 1883. In 1884,
an International Prime Meridian Conference was held in
Washington D.C. to adopt the standardize method of
time keeping and determined the location of the Prime
Meridian. Conference members agreed that the
longitude of Greenwich, England would become zero degrees
longitude and established the 24 time zones relative
to the Prime Meridian. It was also proposed that the
measurement of time on the Earth would be made relative
to the astronomical measurements at the Royal Observatory
at Greenwich. This time standard was called Greenwich
Mean Time ( GMT).
Today, many nations operate
on variations of the time zones suggested by Sir Fleming. Figure
2c-1 describes the various time zones currently used
on the Earth. In this system, time in the various zones
is measured relative the Coordinated
Universal Time ( UTC)
standard at the Prime Meridian. Coordinated
Universal Time became the standard legal reference
of time all over the world in 1972. UTC is determined
from six primary atomic clocks that are coordinated by
the International Bureau of
Weights and Measures ( BIPM) located
in France. The numbers located at the bottom of Figure
2c-1 indicate how many hours each zone is earlier
(negative sign) or later (positive sign) than the Coordinated
Universal Time standard. Also note that national
boundaries and political matters influence the shape
of the time zone boundaries. For example, China uses
a single time zone (eight hours ahead of Coordinated
Universal Time) instead of five different
time zones.
| Figure
2c-1: Modern
standard times zones as measured relative to Coordinated
Universal Time. The numbers located at the
bottom indicate how many hours each zone is earlier
(negative sign) or later (positive sign) than Coordinated
Universal Time. Some nations (for example,
Australia and India) have offset their time zones
by half an hour. This situation is not shown on the
illustration. |
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(d). Topographic Maps
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Introduction
A topographic
map is a detailed and accurate two-dimensional
representation of natural and human-made features on
the Earth's surface. These maps are used for a number
of applications, from camping, hunting, fishing, and
hiking to urban planning, resource management, and
surveying. The most distinctive characteristic of a
topographic map is that the three-dimensional shape
of the Earth's surface is modeled by the use of contour
lines. Contours are imaginary lines that connect
locations of similar elevation. Contours make it possible
to represent the height of mountains and steepness
of slopes on a two-dimensional map surface. Topographic
maps also use a variety of symbols to describe both
natural and human made features such as roads, buildings,
quarries, lakes, streams, and vegetation.
Topographic maps produced by the Canadian
National Topographic System (NTS)
are generally available in two different scales: 1:50,000
and 1:250,000. Maps with a scale of 1:50,000 are relatively
large-scale covering an area approximately 1000 square
kilometers. At this scale, features as small as a single
home can be shown. The smaller scale 1:250,000 topographic
map is more of a general purpose reconnaissance-type
map. A map of this scale covers the same area of land
as sixteen 1:50,000 scale maps.
In the United States, topographic maps have
been made by the United
States Geological Survey ( USGS)
since 1879. Topographic coverage of the United States is
available at scales of 1:24,000, 1:25,000 (metric), 1:62,250,
1:63,360 (Alaska only), 1:100,000 and 1:250,000.
Topographic Map Symbols
Topographic maps use symbols to represent
natural and human constructed features found in the environment.
The symbols used to represent features can be of three
types: points, lines, and polygons. Points are used to
depict features like bridges and buildings. Lines are used
to graphically illustrate features that are linear. Some
common linear features include roads, railways, and rivers.
However, we also need to include representations of area,
in the case of forested land or cleared land; this is done
through the use of color.
The set of symbols used on Canadian
National Topographic System (NTS)
maps has been standardized to simplify the map construction
process. A description of the complete set of symbols
available can be found in a published guide titled: Standards
and Specifications for Polychrome Maps.
This guide guarantees uniform illustration of surface
features on both 1:50 000 and 1:250 000 topographic
maps. Despite the existence of this guide, we can find
that some topographic maps may use different symbols
to depict a feature. This occurs because the symbols
used are graphically refined over time - as a result
the Standards and Specifications
for Polychrome Maps guide is always under
revision.
The tables below describe some of
the common symbols used on Canadian
National Topographic System maps ( source: Centre
for Topographic Information, Natural Resources Canada).
See the following link for
the symbols commonly used on USGS topographic maps.
| Feature Name |
Symbol |
Road - hard surface, all season
|
|
Road - hard surface, all season
|
|
Road - loose or stabilized surface,
all season
|
|
Road - loose surface, dry weather
|
|
Rapid transit route, road
|
|
Road under construction
|
|
Vehicle track or winter road
|
|
Trail or portage
|
|
Traffic circle
|
|
Highway route number
|
|
Transportation Features - Railways and Airports
| Feature Name |
Symbol |
Railway - multiple track
|
|
Railway - single track
|
|
Railway sidings
|
|
Railway - rapid transit
|
|
Railway - under construction
|
|
Railway - abandoned
|
|
Railway on road
|
|
Railway station
|
|
Airfield; Heliport
|
|
Airfield, position approximate
|
|
Airfield runways; paved, unpaved
|
|
Other Transportation Features - Tunnels, Bridges, etc.
| Feature Name |
Symbol |
Tunnel; railway, road
|
|
Bridge
|
|
Bridge; swing, draw, lift
|
|
Footbridge
|
|
Causeway
|
|
Ford
|
|
Cut
|
|
Embankment
|
|
Snow shed
|
|
Barrier or gate
|
|
Hydrographic Features - Human Made
| Feature Name |
Symbol |
Lock
|
|
Dam; large, small
|
|
Dam carrying road
|
|
Footbridge
|
|
Ferry Route
|
|
Pier; Wharf; Seawall
|
|
Breakwater
|
|
Slip; Boat ramp; Drydock
|
|
Canal; navigable or irrigation
|
|
Canal, abandoned
|
|
Shipwreck, exposed
|
|
Crib or abandoned bridge pier
|
|
Submarine cable
|
|
Seaplane anchorage; Seaplane base
|
|
Hydrographic Features - Naturally Occurring
| Feature Name |
Symbol |
Falls
|
|
Rapids
|
|
Direction of flow arrow
|
|
Dry river bed
|
|
Stream - intermittent
|
|
Sand in Water or Foreshore Flats
|
|
Rocky ledge, reef
|
|
Flooded area
|
|
Marsh, muskeg
|
|
Swamp
|
|
Well, water or brine; Spring
|
|
Rocks in water or small islands
|
|
Water elevation
|
|
Terrain Features - Elevation
| Feature Name |
Symbol |
Horizontal control point; Bench
mark with elevation
|
|
Precise elevation
|
|
Contours; index, intermediate
|
|
Depression contours
|
|
Terrain Features - Geology and Geomorphology
| Feature Name |
Symbol |
Cliff or escarpment
|
|
Esker
|
|
Pingo
|
|
Sand
|
|
Moraine
|
|
Quarry
|
|
Cave
|
|
Terrain Features - Land Cover
| Feature Name |
Symbol |
Wooded area
|
|
Orchard
|
|
Vineyard
|
|
Human Activity Symbols - Recreation
Feature Name
|
Symbol
|
Sports track
|
|
Swimming pool
|
|
Stadium
|
|
Golf course
|
|
Golf driving range
|
|
Campground; Picnic site
|
|
Ski area, ski jump
|
|
Rifle range with butts
|
|
Historic site or point of interest;
Navigation light
|
|
Aerial cableway, ski lift
|
|
Human Activity Symbols - Agriculture and Industry
| Feature Name |
Symbol |
Silo
|
|
Elevator
|
|
Greenhouse
|
|
Wind-operated device; Mine
|
|
Landmark object (with height);
tower, chimney, etc.
|
|
Oil or natural gas facility
|
|
Pipeline, multiple pipelines, control
valve
|
|
Pipeline, underground
multiple pipelines, underground
|
|
Electric facility
|
|
Power transmission line
multiple lines
|
|
Telephone line
|
|
Fence
|
|
Crane, vertical and horizontal
|
|
Dyke or levee
|
|
Firebreak
|
|
Cut line
|
|
Human Activity Symbols - Buildings
| Feature Name |
Symbol |
School; Fire station; Police station
|
|
Church; Non-Christian place of
worship; Shrine
|
|
Building
|
|
Service centre
|
|
Customs post
|
|
Coast Guard station
|
|
Cemetery
|
|
Ruins
|
|
Fort
|
|
Contour Lines
Topographic
maps can describe vertical information through
the use of contour
lines (contours). A contour line is an isoline that
connects points on a map that have the same elevation.
Contours are often drawn on a map at a uniform vertical
distance. This distance is called the contour
interval. The map in the Figure 2d-1 shows
contour lines with an interval of 100 feet. Note
that every fifth brown contour lines is drawn bold
and has the appropriate elevation labeled on it.
These contours are called index
contours. On Figure 2d-1 they represent
elevations of 500, 1000, 1500, 2000 feet and so on.
The interval at which contours are drawn on a map
depends on the amount of the relief depicted and
the scale of the map.
| Figure
2d-1: Portion
of the "Tofino" 1:50,000 National
Topographic Series of Canada map. The
brown lines drawn on this map are contour
lines. Each line represents a vertical increase
in elevation of 100 feet. The bold brown contour
lines are called index
contours. The index contours are labeled
with their appropriate elevation which increases
at a rate of 500 feet. Note the blue line drawn to
separate water from land represents an elevation
of 0 feet or sea-level. |
Contour lines provide us with a simple
effective system for describing landscape configuration
on a two-dimensional map. The arrangement, spacing, and
shape of the contours provide the user of the map with
some idea of what the actual topographic configuration
of the land surface looks like. Contour intervals the
are spaced closely together describe a steep slope. Gentle
slopes are indicated by widely spaced contours. Contour
lines that V upwards indicate the presence of a river
valley. Ridges are shown by contours that V downwards.
Topographic Profiles
A topographic
profile is a two-dimensional diagram that
describes the landscape in vertical cross-section.
Topographic profiles are often created from the contour
information found on topographic maps. The simplest
way to construct a topographic profile is to place
a sheet of blank paper along a horizontal transect
of interest. From the map, the elevation of the various
contours is transferred on to the edge of the paper
from one end of the transect to the other. Now on
a sheet of graph paper use the x-axis to represent
the horizontal distance covered by the transect.
The y-axis is used to represent the vertical dimension
and measures the change in elevation along the transect.
Most people exaggerate the measure of elevation on
the y-axis to make changes in relief stand out. Place
the beginning of the transect as copied on the piece
of paper at the intersect of the x and y-axis on
the graph paper. The contour information on the paper's
edge is now copied onto the piece of graph paper. Figure
2d-2 shows a topographic profile drawn from the
information found on the transect A-B above.
| Figure
1d-2: The
following topographic profile shows the vertical
change in surface elevation along the transect AB from Figure
1d-1. A vertical exaggeration of about 4.2 times
was used in the profile (horizontal scale = 1:50,000,
vertical scale = 1:12,000 and vertical exaggeration
= horizontal scale/vertical scale). |
Military Grid Reference System and Map
Location
Two rectangular grid systems are available
on topographic maps for identifying the location of points.
These systems are the Universal
Transverse Mercator ( UTM) grid
system and the Military
Grid Reference System. The Military
Grid Reference System is a simplified form
of Universal Transverse Mercator
grid system and it provides a very quick and
easy method of referencing a location on a topographic
map. On a topographic maps with a scale 1:50,000 and
larger, the Military Grid Reference
System is superimposed on the surface of map
as blue colored series of equally spaced horizontal and
vertical lines. Identifying numbers for each of these
lines is found along the map's margin. Each identifying
number consists of two digits which range from a value
of 00 to 99 ( Figure 2d-3). Each individual square
in the grid system represents a distance of a 1000 by
1000 meters and the total size of the grid is 100,000
by 100,000 meters.
One problem associated with the Military
Grid Reference System is the fact that
reference numbers must be repeated every 100,000 meters.
To overcome this difficulty, a method was devised
to identify each 100,000 by 100,000 meter grid with
two identifying letters which are printed in blue
on the border of all topographic maps (note some
maps may show more than one grid). When making reference
to a location with the Military
Grid Reference System identifying letters
are always given before the horizontal and vertical
coordinate numbers.
| Figure
2d-3: Portion
of a Military Grid Reference
System found on a topographic map. Coordinates
on this system are based on a X (horizontal
increasing from left to right) and Y (vertical
increasing from bottom to top) system. The symbol
depicting a church is located in the square 9194.
Note that the value along the X-axis (easting)
is given first followed by the value on the Y-axis
(northing).
(Source: Centre
for Topographic Information, Natural Resources
Canada). |
Each individual square in the Military
Grid Reference System can be further divided
into 100 smaller squares (ten by ten). This division
allows us to calculate the location of an object
to within 100 meters. Figure 1d-4 indicates
that the church is six tenths of the way between
lines 91 and 92, and four tenths of
the way between lines 94 and 95. Using
these values, we can state that the easting as
being 916 and the northing as 944.
By convention, these two numbers are combined into
a coordinate reference of 916944.
| Figure
2d-4: Further
determination of the location of the church described
in Figure 2d-3. Using the calibrated ruler
we can now suggest the location of the church to
be 916 on the X-axis and 944 on
the Y-axis. Note that the location reference
always has an even number of digits, with the three
digits representing the easting and
the second three the northing.
(Source: Centre
for Topographic Information, Natural Resources
Canada). |
|
(e). Introduction to Remote Sensing
|
|
Remote
sensing can be defined as the collection
of data about an object from a distance.
Humans and many other types of animals accomplish
this task with aid of eyes or by the sense
of smell or hearing. Geographers use the
technique of remote sensing to monitor or
measure phenomena found in the Earth's lithosphere, biosphere, hydrosphere,
and atmosphere.
Remote sensing of the environment by geographers
is usually done with the help of mechanical
devices known as remote
sensors. These gadgets have a greatly
improved ability to receive and record information
about an object without any physical contact.
Often, these sensors are positioned away
from the object of interest by using helicopters,
planes, and satellites. Most sensing devices
record information about an object by measuring
an object's transmission of electromagnetic
energy from reflecting and radiating surfaces.
Remote sensing imagery has many
applications in mapping land-use and cover, agriculture,
soils mapping, forestry, city planning, archaeological
investigations, military observation, and geomorphological
surveying, among other uses. For example, foresters
use aerial photographs for preparing forest cover
maps, locating possible access roads, and measuring
quantities of trees harvested. Specialized photography
using color infrared film has also been used
to detect disease and insect damage in forest
trees.
The simplest form of remote sensing
uses photographic cameras to record information
from visible or near infrared wavelengths
( Table 2e-1). In the late 1800s, cameras
were positioned above the Earth's surface in
balloons or kites to take oblique
aerial photographs of the landscape.
During World War I, aerial
photography played an important role
in gathering information about the position and
movements of enemy troops. These photographs
were often taken from airplanes. After the war,
civilian use of aerial photography from airplanes
began with the systematic vertical imaging
of large areas of Canada, the United States,
and Europe. Many of these images were used to
construct topographic and other types of reference
maps of the natural and human-made features
found on the Earth's surface.
Table
2e-1: Major regions of the electromagnetic
spectrum.
| Region Name |
Wavelength
|
Comments |
| Gamma Ray |
< 0.03
nanometers
|
Entirely absorbed by the Earth's atmosphere
and not available for remote sensing. |
| X-ray |
0.03 to 30 nanometers
|
Entirely absorbed by the Earth's atmosphere
and not available for remote sensing. |
| Ultraviolet |
0.03 to 0.4 micrometers
|
Wavelengths from 0.03 to 0.3 micrometers
absorbed by ozone in
the Earth's atmosphere. |
| Photographic Ultraviolet |
0.3 to 0.4 micrometers
|
Available for remote sensing the Earth.
Can be imaged with photographic film. |
| Visible |
0.4 to 0.7 micrometers
|
Available for remote sensing the Earth.
Can be imaged with photographic film. |
| Infrared |
0.7 to 100 micrometers
|
Available for remote sensing the Earth.
Can be imaged with photographic film. |
| Reflected Infrared |
0.7 to 3.0 micrometers
|
Available for remote sensing the Earth.
Near Infrared 0.7 to 0.9 micrometers. Can
be imaged with photographic film. |
| Thermal Infrared |
3.0 to 14 micrometers
|
Available for remote sensing the Earth.
This wavelength cannot be captured with photographic
film. Instead, mechanical sensors are used
to image this wavelength band. |
| Microwave or Radar |
0.1 to 100 centimeters
|
Longer wavelengths of this band can pass
through clouds, fog, and rain. Images using
this band can be made with sensors that actively emit
microwaves. |
| Radio |
> 100
centimeters
|
Not normally used for remote sensing the
Earth. |
The development of color photography
following World War II gave a more natural depiction
of surface objects. Color aerial photography
also greatly increased the amount of information
gathered from an object. The human eye can differentiate
many more shades of color than tones of gray
(Figure 2e-1 and 2e-2). In 1942,
Kodak developed color infrared film, which recorded
wavelengths in the near-infrared part of the
electromagnetic spectrum. This film type had
good haze penetration and the ability to determine
the type and health of vegetation.
| Figure
2e-1: The
rows of color tiles are replicated in the
right as complementary gray tones. On the
left, we can make out 18 to 20 different
shades of color. On the right, only 7 shades
of gray can be distinguished. |
| Figure
2e-2: Comparison
of black and white and color images of the
same scene. Note how the increased number
of tones found on the color image make the
scene much easier to interpret. (Source: University
of California at Berkley - Earth
Sciences and Map Library). |
Satellite Remote Sensing
In the 1960s, a revolution in remote
sensing technology began with the deployment
of space satellites. From their high vantage-point,
satellites have a greatly extended view of the
Earth's surface. The first meteorological satellite, TIROS-1
( Figure 2e-3), was launched by the United
States using an Atlas rocket on April 1, 1960.
This early weather satellite used vidicon cameras
to scan wide areas of the Earth's surface. Early
satellite remote sensors did not use conventional
film to produce their images. Instead, the sensors
digitally capture the images using a device similar
to a television camera. Once captured, this data
is then transmitted electronically to receiving
stations found on the Earth's surface. The image
below ( Figure 2e-4) is from TIROS-7 of
a mid-latitude
cyclone off the coast of New Zealand.
| Figure
2e-4: TIROS-7
image of a mid-latitude cyclone off the coast
of New Zealand, August 24, 1964. (Source: NASA
- Looking
at Earth From Space). |
Today, the GOES (Geostationary
Operational Environmental Satellite) system of
satellites provides most of the remotely sensed
weather information for North America. To cover
the complete continent and adjacent oceans two
satellites are employed in a geostationary orbit.
The western half of North America and the eastern
Pacific Ocean is monitored by GOES-10, which
is directly above the equator and 135° West
longitude. The eastern half of North America
and the western Atlantic are cover by GOES-8.
The GOES-8 satellite is located overhead of the
equator and 75° West longitude. Advanced
sensors aboard the GOES satellite produce a continuous
data stream so images can be viewed at any instance.
The imaging sensor produces visible and infrared
images of the Earth's terrestrial surface and
oceans ( Figure 2e-5). Infrared images
can depict weather conditions even during the
night. Another sensor aboard the satellite
can determine vertical temperature
profiles, vertical moisture profiles, total precipitable
water, and atmospheric
stability.
| Figure
2e-5: Color
image from GOES-8 of hurricanes Madeline
and Lester off the coast of Mexico, October
17, 1998. (Source: NASA - Looking
at Earth From Space). |
In the 1970s, the second revolution
in remote sensing technology began with the deployment
of the Landsat satellites.
Since this 1972, several generations of Landsat
satellites with their Multispectral
Scanners ( MSS)
have been providing continuous coverage of the
Earth for almost 30 years. Current, Landsat satellites
orbit the Earth's surface at an altitude of approximately
700 kilometers. Spatial resolution of objects
on the ground surface is 79 x 56 meters. Complete
coverage of the globe requires 233 orbits and
occurs every 16 days. The Multispectral Scanner
records a zone of the Earth's surface that is
185 kilometers wide in four wavelength bands:
band 4 at 0.5 to 0.6 micrometers, band 5 at 0.6
to 0.7 micrometers, band 6 at 0.7 to 0.8 micrometers,
and band 7 at 0.8 to 1.1 micrometers. Bands 4
and 5 receive the green and red wavelengths in
the visible light range of the electromagnetic
spectrum. The last two bands image near-infrared
wavelengths. A second sensing system was added
to Landsat satellites launched after 1982. This
imaging system, known as the Thematic
Mapper, records seven wavelength bands
from the visible to far-infrared portions of
the electromagnetic spectrum ( Figure 2e-6).
In addition, the ground resolution of this sensor
was enhanced to 30 x 20 meters. This modification
allows for greatly improved clarity of imaged
objects.
The usefulness
of satellites for remote sensing has resulted
in several other organizations launching their
own devices. In France, the SPOT ( Satellite
Pour l'Observation de la Terre)
satellite program has launched five satellites
since 1986. Since 1986, SPOT satellites have
produced more than 10 million images. SPOT
satellites use two different sensing systems
to image the planet. One sensing system produces
black and white panchromatic images from the
visible band (0.51 to 0.73 micrometers) with
a ground resolution of 10 x 10 meters. The
other sensing device is multispectral capturing
green, red, and reflected infrared bands at 20
x 20 meters ( Figure 2d-7). SPOT-5, which
was launched in 2002, is much
improved from the first four versions of SPOT
satellites. SPOT-5 has a maximum ground resolution
of 2.5 x 2.5 meters in both panchromatic
mode and multispectral operation.
| Figure
2e-7: SPOT
false-color image of the southern portion
of Manhatten Island and part of Long Island,
New York. The bridges on the image are (left
to right): Brooklyn Bridge, Manhattan Bridge,
and the Williamsburg Bridge. (Source: SPOT
Image). |
Radarsat-1
was launched by the Canadian
Space Agency in November, 1995. As a
remote sensing device, Radarsat is quite different
from the Landsat and SPOT satellites. Radarsat
is an active
remote sensing system that transmits
and receives microwave
radiation. Landsat and SPOT sensors passively measure
reflected radiation at wavelengths roughly equivalent
to those detected by our eyes. Radarsat's microwave
energy penetrates clouds, rain, dust, or haze
and produces images regardless of the Sun's illumination
allowing it to image in darkness. Radarsat images
have a resolution between 8 to 100 meters. This
sensor has found important applications in crop
monitoring, defence surveillance, disaster monitoring,
geologic resource mapping, sea-ice mapping and
monitoring, oil slick detection, and digital
elevation modeling ( Figure 2e-8).
| Figure
2e-8: Radarsat
image acquired on March 21, 1996, over Bathurst
Island in Nunavut, Canada. This image shows
Radarsat's ability to distinguish different
types of bedrock. The light shades on this
image (C)
represent areas of limestone, while the darker
regions (B)
are composed of sedimentary siltstone. The
very dark area marked A is
Bracebridge Inlet which joins the Arctic
ocean. (Source: Canadian
Centre for Remote Sensing - Geological
Mapping Bathurst Island, Nunavut, Canada
March 21, 1996). |
Principles of Object Identification
Most people have no problem identifying
objects from photographs taken from an oblique
angle. Such views are natural to the human eye
and are part of our everyday experience. However,
most remotely sensed images are taken from an
overhead or vertical perspective and from distances
quite removed from ground level. Both of these
circumstances make the interpretation of natural
and human-made objects somewhat difficult. In
addition, images obtained from devices that receive
and capture electromagnetic wavelengths outside
human vision can present views that are quite
unfamiliar.
To overcome the potential difficulties
involved in image recognition, professional image
interpreters use a number of characteristics
to help them identify remotely sensed objects.
Some of these characteristics include:
Shape: this
characteristic alone may serve to identify many objects.
Examples include the long linear lines of highways,
the intersecting runways of an airfield, the perfectly
rectangular shape of buildings, or the recognizable
shape of an outdoor baseball diamond ( Figure 2e-9).
| Figure
2e-9: Yankee
stadium in Bronx, New York. Baseball stadiums
have an obvious shape that can be easily
recognized even from vertical aerial
photographs. (Source: Google
Earth). |
Size: noting
the relative and absolute sizes of objects is important
in their identification. The scale of the image determines
the absolute size of an object. As a result, it is
very important to recognize the scale of the image
to be analyzed.
Image Tone or Color:
all objects reflect or emit specific signatures of
electromagnetic radiation. In most cases, related
types of objects emit or reflect similar wavelengths
of radiation. Also, the types of recording device
and recording media produce images that are reflective
of their sensitivity to particular range of radiation.
As a result, the interpreter must be aware of how
the object being viewed will appear on the image
examined. For example, on color infrared images vegetation
has a color that ranges from pink to red rather than
the usual tones of green.
Pattern: many
objects arrange themselves in typical patterns. This
is especially true of human-made phenomena. For example,
orchards have a systematic arrangement imposed by
a farmer, while natural vegetation usually has a
random or chaotic pattern ( Figure 2e-10).
| Figure
2e-10: Black
and white aerial photograph of natural coniferous
vegetation (left) and adjacent apple orchards
(center and right). |
Shadow: shadows
can sometimes be used to get a different view of
an object. For example, an overhead photograph of
a towering smokestack or a radio transmission tower
normally presents an identification problem. This
difficulty can be over come by photographing these
objects at Sun angles that cast shadows. These shadows
then display the shape of the object on the ground.
Shadows can also be a problem to interpreters because
they often conceal things found on the Earth's surface.
Texture: imaged
objects display some degree of coarseness or smoothness.
This characteristic can sometimes be useful in object
interpretation. For example, we would normally expect
to see textural differences when comparing an area
of grass with a field corn. Texture, just like object
size, is directly related to the scale of the image.
|
|
(f). Introduction to Geographic Information Systems
|
|
Introduction and Brief History
The advent of cheap and powerful computers
over the last few decades has allowed for the development
of innovative software applications for the storage,
analysis, and display of geographic data. Many of
these applications belong to a group of software
known as Geographic
Information Systems ( GIS).
Many definitions have been proposed for what constitutes
a GIS. Each of these definitions conforms to the
particular task that is being performed. Instead
of repeating each of these definitions, I would like
to broadly define GIS according to what it does.
Thus, the activities normally carried out on a GIS
include:
-
The measurement of natural and human
made phenomena and processes from a spatial perspective.
These measurements emphasize three types of properties
commonly associated with these types of systems: elements, attributes,
and relationships.
-
The storage of measurements in digital
form in a computer database. These measurements are
often linked to features on a digital map. The features
can be of three types: points, lines, or areas (polygons).
-
The analysis of collected measurements
to produce more data and to discover new relationships
by numerically manipulating and modeling different
pieces of data.
-
The depiction of the measured or
analyzed data in some type of display - maps, graphs,
lists, or summary statistics.
The first computerized GIS began its
life in 1964 as a project of the Rehabilitation and
Development Agency Program within the government
of Canada. The Canada Geographic
Information System (CGIS)
was designed to analyze Canada's national land inventory
data to aid in the development of land for agriculture.
The CGIS project was completed in 1971 and the software
is still in use today. The CGIS project also involved
a number of key innovations that have found their
way into the feature set of many subsequent software
developments.
From the mid-1960s to 1970s, developments
in GIS were mainly occurring at government agencies
and at universities. In 1964, Howard Fisher established
the Harvard Lab for Computer
Graphics where many of the industries
early leaders studied. The Harvard Lab produced a
number of mainframe GIS applications including: SYMAP
(Synagraphic Mapping System),CALFORM, SYMVU, GRID,
POLYVRT, and ODYSSEY. ODYSSEY was first modern vector
GIS and many of its features would form the basis
for future commercial applications. Automatic Mapping
System was developed by the United States Central
Intelligence Agency ( CIA)
in the late 1960s. This project then spawned the
CIA's World Data Bank,
a collection of coastlines, rivers, and political
boundaries, and the CAM software
package that created maps at different scales from
this data. This development was one of the first
systematic map databases. In 1969, Jack Dangermond,
who studied at the Harvard Lab for Computer Graphics,
co-founded Environmental
Systems Research Institute ( ESRI)
with his wife Laura. ESRI would
become in a few years the dominate force in the GIS
marketplace and create ArcInfo and ArcView software.
The first conference dealing with GIS took place
in 1970 and was organized by Roger Tomlinson (key
individual in the development of CGIS)
and Duane Marble (professor at Northwestern University
and early GIS innovator). Today, numerous conferences
dealing with GIS run every year attracting thousands
of attendants.
In the 1980s and 1990s, many GIS applications
underwent substantial evolution in terms of features
and analysis power. Many of these packages were being
refined by private companies who could see the future
commercial potential of this software. Some of the
popular commercial applications launched during this
period include: ArcInfo, ArcView, MapInfo, SPANS
GIS, PAMAP
GIS, INTERGRAPH,
and SMALLWORLD.
It was also during this period that many GIS applications
moved from expensive minicomputer workstations to
personal computer hardware.
Components of a GIS
A Geographic
Information System combines computer
cartography with a database management system. Figure
2f-1 describes some of the major components
common to a GIS. This diagram suggests that a
GIS consists of three subsystems: (1) an input
system that allows for the collection of data
to be used and analyzed for some purpose; (2)
computer hardware and software systems that store
the data, allow for data management and analysis,
and can be used to display data manipulations
on a computer monitor; (3) an output system that
generates hard copy maps, images, and other types
of output.
| Figure
2f-1: Three
major components of a Geographic Information
System. These components consist of input, computer
hardware and software, and output subsystems. |
Two basic types of data are normally
entered into a GIS. The first type of data consists
of real world phenomena and features that have some
kind of spatial dimension. Usually, these data elements are
depicted mathematically in the GIS as either points,
lines, or polygons that are referenced geographically
(or geocoded)
to some type of coordinate system. This type data
is entered into the GIS by devices like scanners,
digitizers, GPS, air photos, and satellite imagery.
The other type of data is sometimes referred to as
an attribute.
Attributes are pieces of data that are connected
or related to the points, lines, or polygons mapped
in the GIS. This attribute data can be analyzed to
determine patterns of importance. Attribute data
is entered directly into a database where it is associated
with element data.
The difference between element and attribute data
can be illustrated in Figures 2f-2 and 2f-3. Figure
2f-2 shows the location of some of the earthquakes that
have occurred in the last century. These plotted
data points can be defined as elements because their
main purpose is to describe the location of the earthquakes.
For each of the earthquakes plotted on this map,
the GIS also has data on their depth. These measurements
can be defined as attribute data because they are
connected to the plotted earthquake locations in Figure
2f-2. Figure 2f-3 shows the attribute
earthquake depth organized into three categories:
shallow; intermediate; and deep. This analysis indicates
a possible relationship between
earthquake depth and spatial location - deep earthquakes
do not occur at the mid-oceanic
ridges.
| Figure
2f-2: Distribution
of earthquake events that have occurred over
the last century. |
| Figure
2f-3: Earthquake
events organized according to depth (yellow (shallow)
= surface to 25 kilometers below the surface, red (intermediate)
= 26 to 75 kilometers below the surface, and black (deep)
= 76 to 660 kilometers below the surface). |
Within the GIS database
a user can enter, analyze, and manipulate data that
is associated with some spatial element in the real
world. The cartographic software of the GIS enables
one to display the geographic information at any
scale or projection and as a variety of layers which
can be turned on or off. Each layer would show some
different aspect of a place on the Earth. These layers
could show things like a road network, topography,
vegetation cover, streams and water bodies, or the
distribution of annual precipitation received. The
output illustrated in Figure 2f-4 merges data
layers for vegetation community type, glaciers and
ice fields, and water bodies (streams, lakes, and
ocean).
| Figure
2f-4: Graphic
output from a GIS. This GIS contains information
about the major plant communities, lakes and
streams, and glaciers and ice fields found occupying
the province of British Columbia, Canada. The
output shows Vancouver Island and part of the
British Columbia mainland. |
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