Author: Jon Willis, MS

A geographic information system (GIS) is a combination of hardware and software that allows a user to create and manipulate geo-referenced data (data that describes places on the earth's surface).

While there are other types of programs that allow users to work with spatial data, they are not considered a GIS as they do not have the capability to express the information in the form of a map (or what Arc View calls a “view”).   A true GIS is able to link geographic data (such as the latitude and longitude of rivers, roads, and towns) with other data (such as population, incidence of disease, or forest types). The key feature of a GIS is that it allows the user to identify spatial relationships between map features.  A GIS does not store a map or view in the form of an image. Rather, a GIS stores data in database form, from which users can create a desired map to suit a particular purpose.  A database can be created that contains the location of a point and or points on the earth and other attributes associated with the points as well.  This “marriage” empowers the user with a particularly powerful tool to represent pictorially geographically referenced tabular information.

Currently, GISs are used as the key analysis and display tool for spatial data, a process called “spatial analysis”.  "Spatial analysis" includes an array of procedures for simplifying, analyzing, and visualizing geo-referenced data. Spatial analysis can be as uncomplicated as taking measurements from a map or as sophisticated statistical analysis of several variables. They are used in applications such as mapping utility infrastructure (routing of gas, water, and electric), land-use mapping (urban planning), analysis and mapping for transportation, and geo-demographic analysis (locating facilities).  Users include county and city governments, state and federal agencies, the health care industry, research institutes, and private industry.

English physician, John Snow, created the first example of the use of mapping in epidemiological research in 1854.  London was in the midst of a cholera outbreak.  He mapped out the locations of those afflicted, and identified the water source responsible for the outbreak.  While this is a primitive model, it is a prime example of how GISs are used in epidemiological research. By tracking incidence, vectors, and other aspects of various diseases, agencies are able to identify populations at-risk, target interventions, and respond more effectively to outbreaks.

Problems in health, economic development, environmental change, and other problems demand that sense be made of what is happening in the world. New remote-sensing satellites are providing unprecedented amounts of data on aspects of the Earth environment, and new sources of demographic, social, and economic data are becoming available at finer spatial detail. Yet our ability to "drink from the firehose," extract meaning, and make useful decisions has not kept pace. We can no longer rely on the human eye and brain alone but must augment their powers through the development of improved techniques for sifting through data to find patterns and outliers, for creating more effective visualizations of data, for testing theories and hypotheses, and for making decisions.