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ToolsGeographic Information Systems (GIS)

Author: Thomas D. Sisk

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Geographic Information Systems allow the overlaying of data layers as diverse as satellite imagery, plant surveys, and bird abundance data. Different data layers can be queried simultaneously, providing deeper insight than might be possible with traditional analytical approaches.

Geographic Information systems (GIS) are the combination of spatially referenced data, appropriate computer hardware and software, and users competent to employ the data and technology to solve problems. GIS is typically used to store and analyze extensive information in a map-based format. This allows relatively easy retrieval and manipulation of information and provides new analytical capabilities based on spatial relationships between sites of interest and any combination of available data sets.

GIS is quickly becoming the data management standard in planning the use of land and natural resources. Virtually all environmental issues involve map-based data, and real-world problems typically extend over relatively large areas. A GIS links observations and measurements to specific locations and specifies the relationships, actual or inferred, between data points. A GIS can pull together very different data types and allow quantitative analysis at the scale of landscapes or entire regions. For example, information on soils, hydrology, and vegetation might be combined in analyses of wildlife habitat needs, and this new data set could be used in planning a strategy for restoration of degraded ecosystems. GIS facilitates the integration of remotely-sensed images with data collected by more traditional means, such as field surveys of vegetation patterns or air and water quality measures, and it permits extrapolation from limited sample locations to larger areas. Because of its ability to handle these complex analyses at large geographic scales, GIS has become an indispensable tool for land and resource managers.

GIS as link a between geography and related sciences

The discipline of geography has a long intellectual history, and geographers have profoundly influenced patterns of immigration, settlement, and land use. The invention of GIS has changed geography’s whole approach to spatial data analysis. The use of GIS with other technologies, such as remote sensing and computer science, has helped geography cross over into other fields such as ecology, forestry, landscape architecture, anthropology, urban planning, and business. The implications of connecting geography with ecology, resource management, and land use planning was articulated by visionary geographers decades ago, perhaps most convincingly by Ian McHarg in his landmark book "Design With Nature". GIS provides the toolbox for realizing the power of McHarg’s vision. In a GIS, landscapes are described as points, lines, areas, volumes – all in terms of their location in a known coordinate system. Diverse data types, be they physical, biological, or cultural, can be incorporated into this landscape representation, using a topology that retains their inherent spatial relationships. These innovations have revolutionized the way we work with spatial data and they we think about maps themselves

Static vs. interactive maps

In plain terms, GIS can be seen as an extension of cartography, the map-maker’s trade. The major innovation has been to make the maps themselves flexible and interactive. In traditional cartography the maps are static, meaning one cannot easily go back to the original information in order to revisit interpretations or try new analyses. These are the types of maps that we tape to the walls of a classroom or bury in the glove box of our vehicles. They are good at conveying information selected by the cartographer, which may or may not be helpful to the map user. Geographic information systems provide the ability to mobilize any number of data sets for particular analyses, and they allow the user to generate maps that address directly a particular question or problem.

Analytical advantages of GIS

Maps are simplified pictures of selected aspects of the real world. Because of the complexity of spatial analysis, land and resource managers, ecologists, and others typically simplify spatial relationships and interactions by assuming that the land surface is much more homogeneous than it is. They also assume that different sites, or different points on a map, are independent of each other – for example, we often assume that the probability of a forest fire at one site is independent of that at another site, 10 Km distant. GIS has made it possible to incorporate the spatial dependence of different sites into the maps themselves. This capability opens up new possibilities for ecological analysis.

  • Analysis of temporal change
  • Determination of spatial coincidence of physical and biological features
  • Analysis of fluxes in energy, nutrients, organisms, etc.
  • Integration of explicit landscapes with simulation models

GIS and land and resource planning on the Colorado Plateau

GIS has given geographers and planners a wholly updated toolbox. This has introduced new capabilities, and with them has come new responsibilities. Traditionally, the cartographer's job has been to create a map, as accurate and helpful as possible, to convey basic facts about an area anyone interested. The GIS analyst's goal also is to make a map, but she is expected go further in analysis, to address specific problems and to retain a flexibility that will allow new and wholly unanticipated analyses to be performed, as needed. In many cases, the GIS analyst works with decision makers to play "what if" games, assessing the expected outcomes of alternative land use decisions. For the Colorado Plateau, this sort of interactive analysis, with all stakeholders at the table, is still somewhere in the future, however, with rapidly improving GIS capabilities, and inclusive policy-making processes that include the public, that future may be quite near.


Klopatek, J. M. and Gardner, R. H., editors. 1999. Landscape ecological analysis: Issues and applications. Springer-Verlag, New York, 400 pp.

Lee, C. T. and Marsh, S. E. 1995. The use of archival Landsat MSS and ancillary data in a GIS environment to map historical change in an urban riparian habitat. Photogrammetric Engineering and Remote Sensing 61: 999-1008.

McHarg, I. L. 1969. Design with nature. Doubleday & Co., Inc, New York, 198 pp.

NASA. "Chaco Canyon, New Mexico." http://www.ghcc.msfc.nasa.gov/archeology/chaco.html 9/23/99.

Ramsey, R. D., Homer, C. G. and Edwards, T. C., Jr. 1993. Gap analysis land cover map for the state of Utah: a hierarchical data base. Pp. 298-306 In: GIS, photogrammetry and modeling: Looking to the future with an eye on the past. American Society of Photogrammetry and Remote Sensing, Bethesda, MD.

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Southwest Data Center, Inc. "Colorado Plateau Data Sharing Test Site" http://www.landuse.com/coplateau/index.html. 10/23/99.

Van West, C. R. 1991. Reconstructing prehistoric climatic variability and agricultural production in southwestern Colorado, A.D. 901-1300: A GIS approach. Pp. 25-34 In: Hutchinson, A., Smith, J. E. and Usher, J., editors. Proceedings of the Anasazi Symposium 1991. Mesa Verde Museum Association, Inc., Mesa Verde, CO.