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Although you may already have some familiarity with what GIS is, it is useful to start with a definition. A geographic information system (GIS) is a specialized computer database program designed for the collection, storage, manipulation, retrieval, and analysis of spatial data. GIS provides far more than the ability to create maps; although maps are a common output of GIS, they are not the only outcome of analysis, and sometimes not even an essential end product. If this surprises you, consider that GIS technology was originally developed in the 1960s, when computer graphics were virtually nonexistent and output was more often printed on hard copy than displayed on monitors. GIS serves as a powerful data collection, organization, exploration, and analysis tool that can assist the researcher in multiple ways. Perhaps its greatest value lies in its ability to help us understand, draw parallels, and see connections between factors and/or variables with an eye for spatial relationships: understanding any situation, problem, or issue necessitates gaining information, and the best way to gain information is through a variety of channels, not by relying on a single source of information that could be error filled. The next section explores what is meant by the term GIS, which facilitates spatial thinking.

In its simplest form, GIS is designed to store, manipulate, analyze, and output map-based, or spatial, information. In practice, the functions of GIS can be carried out by hand, using only paper, pencil, and a ruler (as a surprising number of people still do). Of course, this is not practical or efficient for many research applications.

When we refer to spatial information or data, we mean that the information is linked to a specific location, such as a street address. Figure 1.3 provides an example of a real-life view of the world, as represented in an aerial photograph. This photograph is tied to associated data about the world similar to what you might collect or analyze in a study. These tabular data are related to the world via their location.

Figure 1.3 On the left is an example of a US Geological Survey (USGS) aerial photograph of a suburban location. This shows the world in much the same manner as if you were looking out the window of an airplane. When collecting data in this area, you could record the area’s street address, census block, or neighborhood. These are examples of spatial information. On the right are tabular data associated with one surveyed household, as recorded on a survey form. Used together, spatial and tabular information would be useful in doing GIS-based analysis. Figure by Steven Steinberg, color infrared imagery, USGS National Aerial Photography Program (NAPP), Charleston, SC, acquired February 6, 2007.

Although no single definition of GIS exists, GIS professionals do agree on some general principles. First, GIS requires a combination of computer hardware and software tools. Second, GIS requires data, and these data must possess a spatial or location component. Third, GIS requires knowledgeable individuals to develop the database and carry out the data processing. Although GIS software has become much easier to use since the introduction of graphical user interfaces, GIS programs, and much of the underlying geographic theory, require people to have a basic understanding of maps and map analysis. Anyone with a little basic computer knowledge, which we discuss in this book, can accomplish most GIS tasks. However, for more complex data and analysis, it is often helpful to work with a GIS analyst with in-depth knowledge of GIS and data.

Last, and perhaps most important, GIS is a system for analysis; that is, GIS is useful for examining, displaying, and outputting information gleaned from the data that are stored and maintained in the system. This book explains the necessary mapping concepts and spatial analysis you need to do GIS-based research.