What's Special about a GIS - Lecture Material - Completely GIS dan Remote Sensing tutorial - facegis.com
What's Special about a GIS

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.

A color diagram map with cross hairs on a point.

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.

A black and white screen snapshot showing coordinate information for the point.

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.

A colored section of a map with selected points.

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).


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).

A map showing a network lines in blue.

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.

A black and white map with a network of blue lines overlaying the map.

Figure 18b. Flow superimposed on a digital orthophoquad of the area.


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.

A black and white shaded relief map with an overlay of colored lines.

Figure 19a. Shaded-relief map and contour lines generated from the digital elevation model in the study area.

A color map of slopes in relief with an overlay of colored lines.

Figure 19b. Map showing the steepness of slopes in the study area, created by GIS from the digital elevation model.

A colored map of streams and buffer zones.

Figure 19c. Distances to streams as measured by three 200-meter buffers derived from a digital map of hydrography.

A map with colored shapes representing land use.

Figure 19d. Map indicating various land uses in the study area.

A map with colors representing various soil types.

Figure 19e. A soils map stored in a GIS database. Numbers indicate the type of soil.

A map with colored lines and shapes to represent different zones.

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.

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).

A colored satellite photograph modified by GIS.

A color of a section of a road map.

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.

Source: http://egsc.usgs.gov/isb/pubs/gis_poster/