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|
Geographic Information Systems (GIS) Poster
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Geographic Information Systems
Poster side 1
|| What is GIS?
|| How does a GIS Work?
|| What's Special About a GIS?
||
|| Framework for Cooperation
|| For More Information
||
Poster side 2
|| Applications of GIS
|| GIS Through History
|| GIS Display Techniques
||
Poster side 1
Geographic information system (GIS) technology can be used for scientific investigations,
resource management, and development planning. For example, a GIS might allow emergency
planners to easily calculate emergency response times in the event of a natural disaster, or a GIS
might be used to find wetlands that need protection from pollution.
What is a GIS?
A GIS is a computer system capable of capturing, storing, analyzing, and displaying
geographically referenced information; that is, data identified according to location. Practitioners
also define a GIS as including the procedures, operating personnel, and spatial data that go into
the system.
How does a GIS work?
Relating information from different sources
The power of a GIS comes from the ability to relate different information in a spatial context
and to reach a conclusion about this relationship. Most of the information we have about our
world contains a location reference, placing that information at some point on the globe. When
rainfall information is collected, it is important to know where the rainfall is located. This is done
by using a location reference system, such as longitude and latitude, and perhaps elevation.
Comparing the rainfall information with other information, such as the location of marshes
across the landscape, may show that certain marshes receive little rainfall. This fact may indicate
that these marshes are likely to dry up, and this inference can help us make the most appropriate
decisions about how humans should interact with the marsh. A GIS, therefore, can reveal
important new information that leads to better decisionmaking.
Many computer databases that can be directly entered into a GIS are being produced by
Federal, State, tribal, and local governments, private companies, academia, and nonprofit
organizations. Different kinds of data in map form can be entered into a GIS (figs. 1a, 1b, 1c, 1d,
1e, 1f, and 2). A GIS can also convert existing digital information, which may not yet be in map
form, into forms it can recognize and use. For example, digital satellite images can be analyzed
to produce a map of digital information about land use and land cover (figs. 3 and 4). Likewise,
census or hydrologic tabular data can be converted to a maplike form and serve as layers of
thematic information in a GIS (figs. 5 and 6).
Figure 1a. U.S. Geological Survey (USGS)
digital line graph (DLG) data of roads.
Figure 1b. USGS DLG of rivers.
Figure 1c. USGS DLG of contour lines (hypsography).
Figure 1d. USGS digital elevation (DEM).
Figure 1e. USGS scanned, rectified topographic map called a
digital raster graphic (DRG).
Figure 1f. USGS digital orthophoto quadrangle (DOQ).
Figure 2. USGS geologic map.
Figure 3. Landsat 7 satellite image from which land cover information can be derived.
Figure 4. Satellite image data in figure 3 have been
analyzed to indicate classes of land uses and cover.
Figure 5. Part of a census data file containing address information.
Figure 6. Part of a hydrologic data report indicating the discharge and amount of river flow recorded by a particular streamgage that has a known location.
|| ↑ Top ||
Data capture
How can a GIS use the information in a map? If the data to be used are not already in digital
form, that is, in a form the computer can recognize, various techniques can capture the
information. Maps can be digitized by hand-tracing with a computer mouse on the screen or on a
digitizing tablet to collect the coordinates of features. Electronic scanners can also convert maps
to digits (fig. 7). Coordinates from Global Positioning System (GPS) receivers can also be
uploaded into a GIS (fig. 8).
Figure 7. Scanning paper maps to produce digital data files for input into a GIS.
Figure 8. Collecting latitude and longitude coordinates
with a Global Positioning System (GPS) receiver.
A GIS can be used to emphasize the spatial relationships among the objects being mapped.
While a computer-aided mapping system may represent a road simply as a line, a GIS may also
recognize that road as the boundary between wetland and urban development between two
census statistical areas.
Data capture—putting the information into the system—involves identifying the
objects on the map, their absolute location on the Earth's surface, and their spatial relationships.
Software tools that automatically extract features from satellite images or aerial photographs are
gradually replacing what has traditionally been a time-consuming capture process. Objects are
identified in a series of attribute tables—the "information" part of a GIS. Spatial
relationships, such as whether features intersect or whether they are adjacent, are the key to all
GIS-based analysis.
|| ↑ Top ||
Data integration
A GIS makes it possible to link, or integrate, information that is difficult to associate through any
other means. Thus, a GIS can use combinations of mapped variables to build and analyze new
variables (fig. 9).
Figure 9. Data integration is the linking of information in
different forms through a GIS.
For example, using GIS technology, it is possible to combine agricultural records with
hydrography data to determine which streams will carry certain levels of fertilizer runoff.
Agricultural records can indicate how much pesticide has been applied to a parcel of land. By
locating these parcels and intersecting them with streams, the GIS can be used to predict the
amount of nutrient runoff in each stream. Then as streams converge, the total loads can be
calculated downstream where the stream enters a lake.
|| ↑ Top ||
Projection and registration
A property ownership map might be at a different scale than a soils map. Map information in
a GIS must be manipulated so that it registers, or fits, with information gathered from other
maps. Before the digital data can be analyzed, they may have to undergo other
manipulations—projection conversions, for example—that integrate them into a
GIS.
Projection is a fundamental component of mapmaking. A projection is a mathematical means
of transferring information from the Earth's three-dimensional, curved surface to a
two-dimensional medium—paper or a computer screen. Different projections are used for
different types of maps because each projection is particularly appropriate for certain uses. For
example, a projection that accurately represents the shapes of the continents will distort their
relative sizes.
Since much of the information in a GIS comes from existing maps, a GIS uses the processing
power of the computer to transform digital information, gathered from sources with different
projections, to a common projection (figs. 10a and b).
Figure 10a. An elevation image classified from a satellite
image of Minnesota exists in a different scale and projection than the lines on the digital file of
the State and province boundaries.
Figure 10b. The elevation image has been reprojected to
match the projection and scale of the State and province boundaries.
|| ↑ Top ||
Data structures
Can a land use map be related to a satellite image, a timely indicator of land use? Yes, but
because digital data are collected and stored in different ways, the two data sources may not be
entirely compatible. Therefore, a GIS must be able to convert data from one structure to
another.
Satellite image data that have been interpreted by a computer to produce a land use map can
be "read into" the GIS in raster format. Raster data files consist of rows of uniform cells coded
according to data values. An example is land cover classification (fig. 11). Raster files can be
manipulated quickly by the computer, but they are often less detailed and may be less visually
appealing than vector data files, which can approximate the appearance of more traditional
hand-drafted maps. Vector digital data have been captured as points, lines (a series of point
coordinates), or areas (shapes bounded by lines) (fig. 12). An example of data typically held in a
vector file would be the property boundaries for a particular housing subdivision.
Figure 11. Example of the structure of a raster file.
Figure 12. Example of the structure of a vector data file.
Data restructuring can be performed by a GIS to convert data between different formats. For
example, a GIS can be used to convert a satellite image map to a vector structure by generating
lines around all cells with the same classification, while determining the spatial relationships of
the cell, such as adjacency or inclusion (fig. 13).
Figure 13a. Magnified view of the same
GIS data file, shown in raster format.
Figure 13b. Magnified views of the same
GIS data file. converted into vector format.
|| ↑ Top ||
Data modeling
It is impossible to collect data over every square meter of the Earth's surface. Therefore,
samples must be taken at discrete locations. A GIS can be used to depict two- and
three-dimensional characteristics of the Earth's surface, subsurface, and atmosphere from points
where samples have been collected.
For example, a GIS can quickly generate a map with isolines that indicate the pH of soil
from test points (figs. 14 and 15). Such a map can be thought of as a soil pH contour map. Many
sophisticated methods can estimate the characteristics of surfaces from a limited number of point
measurements. Two- and three-dimensional contour maps created from the surface modeling of
sample points from pH measurements can be analyzed together with any other map in a GIS
covering the area.
Figure 14. Points with pH values of oil.
Figure 15. Contour map made from soil pH values shown in
figure 14.
|| ↑ Top ||
The way maps and other data have been stored or filed as layers of information in a GIS
makes it possible to perform complex analyses.
Figure 16. A crosshair pointer (top) can be used to point at a
location stored in a GIS. The bottom illustration depicts a computer screen containing the kind
of information stored about the location—for example, the latitude, longitude, projection,
coordinates, closeness to wells, sources of production, roads, and slopes of land.
Information retrieval
What do you know about the swampy area at the end of your street? With a GIS you can
"point" at a location, object, or area on the screen and retrieve recorded information about it
from offscreen files (fig. 16). Using scanned aerial photographs as a visual guide, you can ask a
GIS about the geology or hydrology of the area or even about how close a swamp is to the end of
a street. This type of analysis allows you to draw conclusions about the swamp's environmental
sensitivity.
|| ↑ Top ||
Figure 17. Sources of pollution are represented as points.
The colored circles show distance from pollution sources and the wetlands are in dark green.
Topological modeling
Have there ever been gas stations or factories that operated next to the swamp? Were any of
these uphill from and within 2 miles of the swamp? A GIS can recognize and analyze the spatial
relationships among mapped phenomena. Conditions of adjacency (what is next to what),
containment (what is enclosed by what), and proximity (how close something is to something
else) can be determined with a GIS (fig. 17).
Networks
When nutrients from farmland are running off into streams, it is important to know in which
direction the streams flow and which streams empty into other streams. This is done by using a
linear network. It allows the computer to determine how the nutrients are transported
downstream. Additional information on water volume and speed throughout the spatial network
can help the GIS determine how long it will take the nutrients to travel downstream (figs. 18a
and b).
Figure 18a. A GIS can simulate the movement of materials
along a network of lines. These illustrations show the route of pollutants through a stream
system. Flow directions are indicated by arrows.
Figure 18b. Flow superimposed on a digital orthophoquad of
the area.
|| ↑ Top ||
Overlay
Using maps of wetlands, slopes, streams, land use, and soils (figs. 19a-f), the GIS might
produce a new map layer or overlay that ranks the wetlands according to their relative sensitivity
to damage from nutrient runoff.
Figure 19a. Shaded-relief map and contour lines generated
from the digital elevation model in the study area.
Figure 19b. Map showing the steepness
of slopes in the study area, created by GIS from the digital elevation model.
Figure 19c. Distances to streams as measured by three
200-meter buffers derived from a digital map of hydrography.
Figure 19d. Map indicating various land uses in the study
area.
Figure 19e. A soils map stored in a GIS database. Numbers
indicate the type of soil.
Figure 19f. The wetlands in the study area ranked according
to their vulnerability to pollution on the basis of combination of factors evaluated by GIS.
|| ↑ Top ||
Data output
A critical component of a GIS is its ability to produce graphics on the screen or on paper to
convey the results of analyses to the people who make decisions about resources. Wall maps,
Internet-ready maps, interactive maps, and other graphics can be generated, allowing the
decisionmakers to visualize and thereby understand the results of analyses or simulations of
potential events (fig. 20).
Figure 20. Examples of finished maps that can
be generated using a GIS, showing landforms and geology (left) and human-built and physical
features (right).
Framework for cooperation
The use of a GIS can encourage cooperation and communication among the organizations
involved in environmental protection, planning, and resource management. The collection of data
for a GIS is costly. Data collection can require very specialized computer equipment and
technical expertise.
Standard data formats ease the exchange of digital information among users of different
systems. Standardization helps to stretch data collection funds further by allowing data sharing,
and, in many cases, gives users access to data that they could not otherwise collect for economic
or technical reasons. Organizations such as the University Consortium for Geographic
Information Science
(www.ucgis.org) and the Federal Geographic Data
Committee
(www.fgdc.gov) seek to encourage standardization
efforts.
For more information
Good places to learn more about GIS technology and methods include the geography
department of your local university, the GIS site at
www.gis.com, your county planning
department, your state department of natural resources, or a
USGS Earth Science Information
Center (ESIC). To locate your nearest ESIC, call 1-888-ASK-USGS, visit
ASK-USGS web site, or visit
www.usgs.gov.
|| ↑ Top ||
Poster side 2
Figure 1. Group of stags (cave painting), Lascaux Caves,
France (Art Resources, N.Y.).
GIS through history
Some 35,000 years ago, Cro-Magnon hunters drew pictures of the animals they hunted on
the walls of caves near Lascaux, France, (fig. 1). Associated with the animal drawings are track
lines and tallies thought to depict migration routes. These early records followed the two-element
structure of modern geographic information systems (GIS): a graphic file linked to an attribute
database.
Figure 2. Tracks of caribou routes in Alaska from April 1985
to December 1986 (U.S. Fish and Wildlife Service).
Today, biologists use collar transmitters and satellite receivers to track the migration routes
of caribou and polar bears to help design programs to protect the animals. In a GIS, the migration
routes were indicated by different colors for each month for 21 months (fig. 2). Researchers then
used the GIS to superimpose the migration routes on maps of oil development plans to determine
the potential for interference with the animals.
|| ↑ Top ||
Mapmaking
Researchers are working to incorporate the mapmaking processes of traditional cartographers
into GIS technology for the automated production of maps.
One of the most common products of a GIS is a map. Maps are generally easy to make using
a GIS and they are often the most effective means of communicating the results of the GIS
process. Therefore, the GIS is usually a prolific producer of maps. The users of a GIS must be
concerned with the quality of the maps produced because the GIS normally does not regulate
common cartographic principles. One of these principles is the concept of generalization, which
deals with the content and detail of information at various scales. The GIS user can change scale
at the push of a button, but controlling content and detail is often not so easy. Mapmakers have
long recognized that content and detail need to change as the scale of the map changes. For
example, the State of New Jersey can be mapped at various scales, from the small scale of
1:500,000 to the larger scale of 1:250,000 and the yet larger scale of 1:100,000 (fig.3a), but each
scale requires an appropriate level of generalization (figs. 3b, c, and d).
Figure 3a. Digital revision of 1:100,000-scale digital line
graph data to produce a 1:500,000-scale New Jersey State base map. Paneling and generalization
are shown in three stages from 1:100,000 scale to 1:250,000 scale to 1:500,000 scale.
Figure 3b, c, d. These digital maps of Bergen County, N.J. are
all at the scale of 1:500,00. The information content of the maps has been reduced through the
process of generalization in two stages, from 1:100,000 scale on the left to 1:250,000 in the
center, then from 1:250,000 to 1:500,00 scale on the right.
|| ↑ Top ||
Site selection
The U.S. Geological Survey (USGS), in a cooperative project with the Connecticut
Department of Natural Resources, digitized more than 40 map layers for the areas covered by the
USGS Broad Brook and Ellington 7.5-minute topographic quadrangle maps (fig. 4). This
information can be combined and manipulated in a GIS to address planning and natural resource
issues. GIS information was used to locate a potential site for a new water well within half a mile
of the Somers Water Company service area (fig. 5).
Figure 4. USGS digital line graph map of the State of
Connecticut from 1:2,000,000-scale data. The Broad Brook and Ellington 7.5-minute quadrangle
areas are outlined in black in the upper middle.
Figure 5. Map of the areas covered by the Broad Brook and
Ellington 7.5-minute quadrangle showing the Somers Water Company service area at the scale of
1:24:000.
To prepare the analysis, cartographers stored digital maps of the water service areas in the
GIS. They used the proximity function in the GIS to draw a half-mile buffer zone around the
water company service area (fig. 6). This buffer zone was the "window" used to view and
combine the various map coverages relevant to the well site selection.
Figure 6. Enlarged view of figure 5 showing a half-mile
buffer zone drawn around the service area of the Somers Water Company.
The land use and land cover map for the two areas shows that the area is partly developed
(fig. 7). A GIS was used to select undeveloped areas from the land use and land cover map as the
first step in finding well sites. The developed areas were eliminated from further consideration
(fig. 8).
Figure 7. Land use and land cover data for the area bounded
by a half-mile buffer zone around the water company service area.
Figure 8. Land use and land cover data shown in figure 7
have been reselected to eliminate developed areas.
The quality of water in Connecticut streams is closely monitored. Some of the streams in the
study area were known to be unusable as drinking water sources. To avoid pulling water from
these streams into the wells, 100-meter buffer zones were created around the unsuitable streams
using the GIS, and the zones were plotted on the map (fig. 9). The map showing the buffered
zones was combined with the land use and land cover map to eliminate areas around unsuitable
streams from the analysis (fig. 10). The areas in blue have the characteristics desired for a water
well site.
Figure 9. Buffer zones of 100 meters are drawn around
polluted stream in the water service area.
Figure 10. Buffered streams shown in figure 9 area subtracted
from areas previously selected with the land use and land cover data.
Point sources of pollution are recorded by the Connecticut Department of Natural Resources.
These records consist of a location and a text description of the pollutant (fig. 11). To avoid these
toxic areas, a buffer zone of 500 meters was established around each point (fig. 12). This
information was combined with the previous two map layers to produce a new map of areas
suitable for well sites (fig. 13).
Figure 11. Points sources of pollution in the water service
area are identified and entered into a GIS.
Figure 12. Buffer zones of 500 meters are drawn around the
point sources of pollution.
Figure 13. A new map is created in a GIS by eliminating the
buffered sources of pollution from the previously selected areas shown in figure 10.
The map of surficial geology shows the earth materials that lie above bedrock (fig. 14). Since
the area under consideration in Connecticut is covered by glacial deposits, the surface consists
largely of sand and gravel, with some glacial till and fine-grained sediments. Of these materials,
sand and gravel are the most likely to store water that could be tapped with wells. Areas
underlain by sand and gravel were selected from the surficial geology map (fig. 15). They were
combined with the results of the previous selections to produce a map consisting of: (1) sites in
underdeveloped areas underlain by sand and gravel, (2) more than 500 meters from point sources
of pollution, and (3) more than 100 meters from unsuitable streams (fig. 16).
Figure 14. Map of surficial geology of the water service area.
Figure 15. Selection areas of sand and gravel from the map of
surficial geology.
Figure 16. Map produced by combining the areas composed
of sand and gravel with previous selection from figure 13.
A map that shows the thickness of saturated sediments was created by using the GIS to
subtract the bedrock elevation from the surface elevation (fig. 17). For this analysis, areas
having more than 40 feet of saturated sediments were selected and combined with the previous
overlays.
Figure 17. A bedrock elevation subtracted from surface
elevation by a GIS to show the thickness of water-saturated sediment.
Figure 18. Potential sites with saturated thickness of
sediments greater than 40 feet.
The resulting site selection map shows areas that are undeveloped, are situated outside the
buffered pollution areas, and are underlain by 40 feet or more of water-saturated sand and gravel
(fig. 18). Because of map resolution and the limits of precision in digitizing, the very small
polygons (areas) may not have all of the characteristics analyzed, so another GIS function was
used to screen out areas smaller than 10 acres. The final six sites are displayed with the road and
stream network and selected place names for use in the field (fig. 19).
Figure 19. Potential water well sites, roads, streams and place names.
The process illustrated by this site selection analysis has been used for many common
applications, including transportation planning and waste disposal site location. The technique is
particularly useful when several physical factors must be considered and integrated over a large
area.
|| ↑ Top ||
Emergency response planning
The Wasatch Fault zone runs through Salt Lake City along the foot of the Wasatch
Mountains in north-central Utah (fig. 20).
Figure 20. Map of the area surrounding the USGS Sugar
House 7.5-minute quadrangle, Salt lake City, Utah, showing the location of the Wasatch Fault zone.
A GIS was used to combine road network and earth science information to analyze the effect
of an earthquake on the response time of fire and rescue squads. The area covered by the USGS
Sugar House 7.5-minute topographic quadrangle map was selected for the study because it
includes both undeveloped areas in the mountains and a part of Salt Lake City. Detailed earth
science information was available for the entire region.
The road network from a USGS digital line graph includes information on the types of roads,
which range from rough trails to divided highways (fig. 21). The locations of fire stations were
plotted on the road network. A GIS function called network analysis was used to calculate the
time necessary for emergency vehicles to travel from the fire stations to different areas of the
city. The network analysis function considers two elements: (1) distance from the fire station,
and (2) speed of travel based on the type of road. The analysis shows that under normal
conditions, most of the area within the city will be served in less than 7 minutes and 30 seconds
because of the distribution and density of fire stations and the continuous network of roads.
The accompanying illustration (fig. 22) depicts the blockage of the road network that would
result from an earthquake, assuming that any road crossing the fault trace would become
impassable. The primary effect on emergency response time would occur in neighborhoods west
of the fault trace, where travel times from the fire stations would be noticeably lengthened.
Figure 21. Before faulting. Road network of area covered by
the Sugar House quadrangle plotted from USGS digital line graph data, indicating the locations
of fire stations and travel times of emergency vehicles. Areas in blue can receive service within
2½minutes, area in green within 5 minutes, areas in yellow within 7½ minutes, and
areas in magenta within 10 minutes. Areas in white cannot receive service within 10 minutes.
Figure 22. After faulting, initial model. Network analysis in
a GIS produces a map of travel times from the stations after faulting. The fault is in red.
Emergency response times have increased for areas west of the fault.
The Salt Lake City area lies on lake sediments of varying thicknesses. These sediments range
from clay to sand and gravel, and most are water-saturated. In an earthquake, these materials may
momentarily lose their ability to support surface structures, including roads. The potential for
this phenomenon, known as liquefaction, is shown in a composite map portraying the inferred
relative stability of the land surface during an earthquake. Areas near the fault and underlain by
thick, loosely consolidated, water-saturated sediments will suffer the most intense surface motion
during an earthquake (fig. 23). Areas on the mountain front with thin surface sediments will
experience less additional ground acceleration. The map of liquefaction potential was combined
with the road network analysis to show the additional effect of liquefaction on response
times.
The final map shows that areas near the fault, as well as those underlain by thick,
water-saturated sediments, are subject to more road disruptions and slower emergency response
than are other areas of the city (fig. 24).
Figure 23. Map of potential ground l liquefaction during an
earthquake. The least stable areas are shown by yellows and oranges, the most stable by grays
and browns.
Figure 24. After faulting, final model. A map showing the
effect of an earthquake on emergency travel times is reduced by combining the liquefaction
potential information from figure 23 with the network analysis from figure 22.
|| ↑ Top ||
Three-dimensional GIS
To more realistically analyze the effect of the Earth's terrain, we use three-dimensional
models within a GIS. A GIS can display the Earth in realistic, three-dimensional perspective
views and animations that convey information more effectively and to wider audiences than
traditional, two-dimensional, static maps. The U.S. Forest Service was offered a land swap by a
mining company seeking development rights to a mineral deposit in Arizona's Prescott National
Forest. Using a GIS, the USGS and the U.S. Forest Service created perspective views of the area
to depict the terrain as it would appear after mining (fig. 25).
Figure 25. Prescott National Forest, showing altered
topography due to mine development.
To assess the potential hazard of landslides both on land and underwater, the USGS
generated a three-dimensional image of the San Francisco Bay area (fig. 26). It created the image
by mosaicking eight scenes of natural color composite Landsat 7 enhanced thematic mapper
imagery on California fault data using approximately 700 digital elevation models at 1:24,000
scale.
Figure 26. Three-dimensional image of the San Francisco
Bay created to assess the potential of land and underwater avalanches.
Graphic display techniques
Traditional maps are abstractions of the real world; each map is a sampling of important
elements portrayed on a sheet of paper with symbols to represent physical objects. People who
use maps must interpret these symbols. Topographic maps show the shape of the land surface
with contour lines. Graphic display techniques in GISs make relationships among map elements
more visible, heightening one's ability to extract and analyze information.
Two types of data were combined in a GIS to produce a perspective view of a part of San
Mateo County, Calif. The digital elevation model, consisting of surface elevations recorded on a
30-meter horizontal grid, shows high elevations as white and low elevations as black (fig. 27).
The accompanying Landsat thematic mapper image shows a false-color infrared image of the
same area in 30-meter pixels, or picture elements (fig. d). A GIS was used to register and
combine the two images to produce the three-dimensional perspective view looking down the
San Andreas Fault (fig. 29).
Figure 27. Digital elevation model of San Mateo County,
Calif.
Figure 28. Landsat Thematic Mapper image of San Mateo
County, Calif.
Figure 29. Perspective view of San Mateo County,
Calif.
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Visualization
Maps have traditionally been used to explore the Earth. GIS technology has enhanced the
efficiency and analytical power of traditional cartography. As the scientific community
recognizes the environmental consequences of human activity, GIS technology is becoming an
essential tool in the effort to understand the process of global change. Map and satellite
information sources can be combined in models that simulate the interactions of complex natural
systems.
Through a process known as visualization, a GIS can be used to produce images—
not just maps, but drawings, animations, and other cartographic products. These images allow
researchers to view their subjects in ways that they never could before. The images often are
helpful in conveying the technical concepts of a GIS to nonscientists.
Adding the element of time
The condition of the Earth's surface, atmosphere, and subsurface can be examined by feeding
satellite data into a GIS. GIS technology gives researchers the ability to examine the variations in
Earth processes over days, months, and years. As an example, the changes in vegetation vigor
through a growing season can be animated to determine when drought was most extensive in a
particular region. The resulting normalized vegetation index represents a rough measure of plant
health (fig. 30). Working with two variables over time will allow researchers to detect regional
differences in the lag between a decline in rainfall and its effect on vegetation. The satellite
sensor used in this analysis is the advanced very high resolution radiometer (AVHRR), which
detects the amounts of energy reflected from the Earth's surface at a 1-kilometer resolution
twice a day. Other sensors provide spatial resolutions of less than 1 meter.
Figure 30. One time slice of the vegetation index
for part of the globe from AVHRR data.
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Serving GIS over the Internet
Through Internet map server technology, spatial data can be accessed and analyzed over the
Internet. For example, current wildfire perimeters are displayed with a standard web browser,
allowing fire managers to better respond to fires while in the field and helping homeowners to
take precautionary measures (fig. 31).
Figure 31. Wildfires burning for the past 24 hours accessible
by means of a web browser and Internet map server GIS technology.
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The future of GIS
Environmental studies, geography, geology, planning, business marketing, and other
disciplines have benefitted from GIS tools and methods. Together with cartography, remote
sensing, global positioning systems, photogrammetry, and geography, the GIS has evolved into a
discipline with its own research base known as geographic information sciences. An active GIS
market has resulted in lower costs and continual improvements in GIS hardware, software, and
data. These developments will lead to a much wider application of the technology throughout
government, business, and industry.
GIS and related technology will help analyze large datasets, allowing a better understanding
of terrestrial processes and human activities to improve economic vitality and environmental
quality.
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Geological Survey. Some figures have been modified or added to improve the scientific
visualization of information.
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