GIS is the ability to conceptualize the geographic relationships between multiple
data sets. GIS is very much to the point of answering the essential geographic
question of “What is where?” Also, it can aid in exploring the relative location
of features and model the likelihood of encountering a particular feature (e.g., suit-
able bird habitat) using a combination of spatial data layers.
The idea behind GIS is simple enough. Suppose a developer wishes to build a
large group of single family houses on a large tract. It is known that some of the
land is boggy, some on the floodplain, and some within areas a county has zoned
for commercial development. The developer would like to avoid each of these
types of areas in situating his/her houses. Whereas the developer could examine
paper maps of each of these three patterns and attempt to associate them by flip-
ping between the maps, GIS provides a rational manner of simultaneously exclud-
ing unsuitable areas and highlighting the suitable areas. Mathematically, it is a
spatial version of Venn diagrams in which the three spatial layers are laid over
the tract and the areas not exhibiting one of the three limitations are deemed suit-
able and automatically mapped.
The applications of GIS have become quite diverse. For instance, GIS has been
applied to modeling of runoff and evapotranspiration, the solution of least-cost
transportation problems, decisions as to which agricultural land is to be idled,
the siting of wind farms, realignment of census boundaries, the exploration for
oil and natural gas, city evacuation plans, location of new retail outlets, and con-
struction of ecoregions. Most cities and agencies of state and federal government
now have GIS operations. Thousands of private companies have followed along.
The opportunity of employment using GIS has exponentially increased and has
dramatically altered the employment landscape within the discipline of geography.
There are many opportunities for programmers, butgeographersare useful
because of their knowledge of cartography plus their knowledge of the spatial pat-
terns of the human and physical landscapes. This employability has changed
undergraduate and graduate geographic education to incorporate formalized
courses and degrees.
Although the premise of GIS seems simple, the implementation of GIS has
some profound implications. The inputs to GIS are electronic, spatially referenced
data sets. That is, the data set is divided into areas and each area is identified by
coordinates so that all areas in the data set can be portrayed on a map. The areas
(in raster or vector styles as defined below) are assigned one or more attributes.
Examples of attributes are elevation, population, land parcels, type of vegetative
cover, presence of a road, or average temperature. The type and number of attrib-
utes assigned are a function of the purpose of that particular GIS.
The design of any major project must be done with care. Choices made early on
can limit the utility of the products and not readily rectified. The sources of GIS data142 Geographic Information Systems