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| GIS history
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GIS through history |
On the walls of caves near
Lascaux,
France, Cro-Magnon hunters drew pictures of the animals they hunted
35,000 years ago.
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: a graphic file
linked to an attribute database.
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.
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. |
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Mapmaking |
Researchers are working to incorporate
the mapmaking experience of traditional cartographers into GIS
technology for the automated production of maps.
Using a GIS and digital version of the 1:100,000 - scale transportation
network, political boundaries, and hydrographic features, cartographers
produced a 1:500,000 - scale standard base map of New Jersey. This
digital revision was done in three steps of map scale reduction:
1:100,000, 1:250,000, and 1:500,000.
Each scale reduction required edge matching, or paneling, of the larger
scale maps to produce the next small-scale map. In addition, through the
generalization process, the amount of information was reduced
to make the smaller scale map readable. |
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Emergency response planning |
The Wasatch Fault zone runs through
Salt Lake City along the foot of the Wasatch Mountains in north-central
Utah.
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 portion of Salt
Lake City. Detailed earth science information was available for the
entire area.
The road network from a USGS digital line graph includes information on
the types of roads, which range from rough trails to divided highways.
The locations of fire stations were plotted on the road network, and 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 tow
elements: distance from the fire station, and speed of travel based on
road type. 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 depicts the blockage of the road network
that would result from an earthquake by 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 lengthened
noticeably.
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.
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. |
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Simulating environmental effects |
The National Forest Service was
offered a land swap by a mining company seeking development rights to a
mineral deposit in the Prescott National Forest of Arizona. Using a GIS
and a variety of digital maps, the USGS and the Forest Service created
perspective views of the area to depict the terrain before and after
mining.
Existing digital data were combined in a GIS and displayed using a
function that creates perspective drawings.
The mining company provided planimetric (two-dimensional) drawings of
the proposed mine.
This plan was digitized, along with elevation information on the
proposed mine and associated piles and ponds. The resulting perspective
view illustrates the dramatic changes to the topography that mining
would cause.
A GIS can combine map types and display them in realistic
three-dimensional perspective views that convey information more
effectively and to wider audiences than traditional, two-dimensional
maps. |
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Graphic display techniques |
Traditional maps are abstractions of
the real world, 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 land
surface with contour lines. The actual shape of the land can be seen
only in the mind's eye. Graphic display techniques in GIS's make
relationships among map elements visible, heightening one's ability to
extract and analyze information.
Two types of data were combined in a GIS to produce a perspective view
or a portion of San Mateo County, California. The digital elevation
model, consisting of surface elevations recorded on a 30-meter
horizontal grid, shows high elevations as white and low elevation as
black.
The accompanying Landsat Thematic Mapper image shows a false-color
infrared image of the same area in 30-meter pixels, or picture elements.
A GIS was used to register and combine the two images to produce the
three-dimensional perspective view looking down the San Andreas Fault. |
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