1.2: Definitions Of Geographic Information Systems (GIS)

Let’s define GIS first.

Definition #1

Over the past 20 to 30 years, many authors (Dept of the Environment, 1987; Rhind, 1988; Parker, 1988; and Bolstad, 2002) have defined GIS, and most of their definitions are similar to one another. The definitions generally refer to a system of computer hardware, software, and people that support the capture, management, analysis, and display of spatial data.

It is a decent definition, but to understand GIS better, you should break it down into its four main subsystems the way Marble and Peuquet (1983) did in perhaps the first widely used GIS textbook. GIS have:

Figure 1.1: The four GIS subsystems.

Much of this e-text is divided into chapters that mirror these four GIS subsystems. Chapter 2 looks at data and the data input system. Chapters 3 and 4 focus on the graphic and database portions of GIS software. These two chapters finish by covering various “housecleaning” processes (preprocessing functions) that manipulate the data files to make them ready for analysis. Chapter 5 looks at how to analyze the datasets. Output is covered in Chapter 6.

Definition #2

An even shorter definition equates GIS to a “spatial database”, but you must focus on both of those words carefully. To do this, think of a computer screen displaying a simple parcel map.

Figure 1.2: The two parts of a GIS.

Each parcel is a separate feature on the map, but they are more than just features on the screen, the computer stores many database characteristics about the feature like the parcel’s identification number and its owner’s name. In other words, there are two parts to a GIS: a map (or spatial) component and an attribute (or database) component. By making this link between the map and the stored attributes, GIS becomes a powerful tool for addressing and analyzing geographic data and environmental issues. This is its appeal. GIS programs are capable of handling large and diverse geographic datasets, and we increasingly rely upon them for analyzing and making decisions.

The two definitions above emphasize GIS as a computer system; a simple definition for a computer system differs only in that GIS handles spatial data. Although the second definition gets closer, both definitions, do not give adequate weight to the geographic component of GIS.

Definition #3

It is no accident that GIS begins with G. A good understanding of GIS begins with geography and specifically with a geographic perspective, which is a way of organizing and thinking about portions of the Earth spatially. Again, look at the map above. You know that it and many other maps depict the locations of people and things (like roads, important buildings, parks, etc.). You also know that there are connections or relationships between the people and things drawn on the map. These relationships help explain the spatial patterns you see on the map. The process of finding, showing, explaining, and even predicting geographic patterns is at the heart of both geography and GIS.

In this context, GIS can be defined as a tool of exploration that helps us explore geographic (or spatial) patterns. At a minimum, it aids us in describing these patterns, but GIS can go beyond simply description to help us investigate and understand why these patterns (sometimes called distributions) exist, the impacts these patterns have on our life and land, and to discover potential future geographic patterns.

You can address five types of geographic questions with GIS and other geotechnologies (ESRI, 1992, pp):

1. What is at…? This basic question looks at what is at a particular location. An example might include, what is at the corner of Main Street and 12th Avenue?
2. Where is it? This question could simply inquire as to the location of something specific (like the nearest market or bookstore), or it can be a more challenging question that explores what locations meet a specific condition. For example, a city might identify all of the parcels that are larger than 5 acres, vacant, zoned commercial, and within ½ mile of a freeway on-ramp.
3. What has changed since? Over a portion of the Earth’s surface, how have conditions changed over time? An example is a county that identifies wetland areas that have decreased in size over the past 10 years.
4. What spatial patterns exist? This question describes and compares spatial patterns at different locations. It attempts to find spatial patterns—perhaps the concentration of phenomena. The process of finding, showing, and explaining geographic patterns is frequently termed spatial analysis. Stewart Fotheringham defines spatial analysis as manipulating spatial data to extract additional meaning. In a GIS context, spatial analysis asks two questions:
   1. What is the relationship between two or more datasets that occupy the same location? For instance, you might see a direct relationship between a region’s varying elevation and the amount of rainfall that falls across it.
   2. What geographic variations exist over space? All geographic phenomena vary in their intensity over space. Consider fertility rates across the United States. Some areas are high and others low. To answer this question fully, you need to describe and explain these patterns.
5. What if…? “What if?” questions involve scenarios that differ when you change the model’s parameters. An example includes looking at what happens to an area’s population when a freeway is built through the area under different constraints.

These questions examine relationships among various geographic phenomena, and you use GIS and other geotechnologies to explore and help you answer these questions. As the geographer Ron Abler states, “GIS technology is to geographical analysis what the microscope, the telescope, and computers have been to other sciences…” (1988, 40). No other technology looks so closely at the spatial relationship of phenomena, and it aids geographers and others that use spatial data to describe, analyze, and predict spatial relationships and patterns. As the geographer Michael DeMers states, “We can now see deeper and farther than we could before, allowing us to map more of what is present on the landscape and to ask questions that could not have been imagined” (2003, 3).