Before we begin the process of learning what GIS is and does, this simple example of using maps to make decisions should give you valuable insight. Suppose you are given the task of determining where, in a particular region, a new town should be developed from scratch in the wilderness (but not too far from civilization) that will be used to house people with various connections to opening a major new mine extracting uranium ore. After pondering the problem, you conclude that the best way to start would be to acquire some maps that include the areas near the eventual mine. These maps could include these thematic types:
You also deduce that you will need other kinds of information, such as on file in government offices. This ancillary info could be land ownership, available sources of power, sewage, etc, highway maintenance, and the like. When all this is collected, what do you do? You lay out the maps, become familiar with their contents, and start looking for potential sites proximate to the future mine. You shift back and forth from map to map trying to find appropriate clues as to where the best site(s) would be. This requires a sort of mental overlay process, which is difficult. After narrowing possibilities, you then feed in pertinent ancillary information. Finally, you arrive at a decision, but this is still subjective and based largely on a qualitative assessment. The whole process is cumbersome, tedious, and generally inefficient.
But what if there is some kind of "automated decision making" that allows you to systematically combine the information in individual maps into an interrelated composite that handles diverse data, embellishes that with relevant ancillary data, and then uses a logical program that quantifies the process of final choice as to the most optimal location. That is precisely what GIS is all about. GIS is the outgrowth of the computer age, and the ease with which data can be manipulated by scanning and other input methodology. GIS centers on maps and other kinds of spatial displays - the starting point in our discussion of this new technology.
Before you proceed through this Section, you could benefit from the Overview of the use of remote sensing together with GIS by decision makers found at this UN FAO web site (note: click on its Introduction link to go to its beginning).
Throughout this Tutorial, we have presented photos and images of the Earth's surface and clouds, some accompanied by maps that locate, classify and describe objects thereon. All these objects share a common characteristic: they are visual, miniaturized representatives, or surrogates, of places and classes of features located geospatially on or above the surface, be it land or water. They thus depict aspects of the local, regional, or global geography, which we can locate geometrically in an x, y (horizontal), and z (vertical) plot. We can reference the plot, then, to some form of coordinate and projection system. A map projection is a specific way of transferring points or locations from a spherical globe onto a scaled-down flat surface (the map) according to a systematic, orderly realignment, using a latitude/longitude grid network.
Photos (images) and maps are inherently two-dimensional or planimetric, although we can use techniques, such as contours or shading, to present a quasi-three-dimensional appearance or to extract information about relative elevations above generalized datum planes. The most common type of three-dimensional map is the topographic map, which we already examined in Section 11 (page 11-1). As we noted in Sections 10 and 11, maps in general nearly always have the following, essential information: graphic distance measures, scale, orientation and direction, projection type, and some geographic coordinate system, along with other descriptors and symbols in an accompanying legend. Topographic maps also have contour intervals.
Maps are manmade derivatives made from aerial photos and space images or by surveying their features on the ground, designed to record information of various kinds about the spatial distribution of the specific categories of features present on the surface. A category can also be a theme. We also refer to other categories called attributes, which are general descriptors that are inherently non-spatial (they depend on characteristics rather than the location). A parcel of land, regardless of size, likely contains a diverse mix of features or characteristics that we can assign to different categories; in other words, it has many attributes. We may need a wide variety of thematic maps and associated attributes to fully describe the contents of a surface. Thus, given an area of, say, one square kilometer, one map may display road networks, another vegetation cover, a third dwellings or functional buildings, a fourth engineering properties suited for excavation, and so forth. We may combine several themes on a multipurpose map, such as show together roads, buildings, recreational areas, etc. One common type of map shows land cover, which identifies all appropriate classes or categories that we wish to display within the map scale limits at selected points or locations. A variant of this map is the land use map that differs by detailing aspects of the cover involved in, or of interest to, human activities.
Examples of land cover or condition maps, each devoted to a single purpose or theme, appear here for slopes, soils, and vegetation, distributed over the southern part of Washoe County in western Nevada (the city of Reno lies near the center):
These maps describe natural states of either the surface or materials underlying it. (Note: as we reduce these maps to fit the web page, information in their legends becomes too small to read. However, the importance of the illustration is in the differing patterns rather than the specific identifiers.) Much of the surface is undeveloped, but areas where people constructed buildings, in which to live, work, manufacture, or play, comprise one form of land use, as shown in this map.
Some maps are composites of conventional, spatial distributions and graphs or other modes of data representation. Here is an example showing an area between Houston and Galveston, Texas, in which average monthly rainfall for the years 1965-67 at selected localities appears as bar graphs:
Thematic maps can cover small areas such as a town or township or county or they can apply to an entire country. Here is a Landsat TM image mosaic that includes South Africa and some neighboring countries.
The next four examples of thematic maps for South Africa are self-explanatory. Taken together, they could be used to decide where to set up farming centers devoted to animal husbandry.
These maps were produced by the Agricultural Research Council - Institute for Soil, Climate, and Water, as displayed in Volume 19 of the ESRI ArcInfo Map Book Gallery .
The Map Book Gallery is worth your time to visit. It contains a wide variety of illustrations of different map types and uses. GIS is a large subset of the general way in which maps are used to store and present data that have geospatial significance. As will be shown later in this Section, a major objective of GIS is to use a wide range of geographically-based input to solve problems and make decisions. But often the maps produced can almost be stand-alone presentations of information that need not be tied to some practical outcome. To illustrate this idea, here are some typical maps from the Gallery which have worthwhile information per se; check their captions for specific descriptions: