Geographic Information Systems

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The dawning of GIS can legitimately be traced back to the beginning of the human race. The earliest known map dates back to 2500 B.C.E., but there were probably maps before that time. Since then, humans have been continually improving the methods of conveying spatial information. The mid-eighteenth century brought the use of map overlays to show troop movements in the Revolutionary War. This could be considered an early GIS. The first British census in 1825 led to the science of demography, another application for GIS. During the 1800s, many different cartographers and scientists were all discovering the power of overlays to convey multiple levels of information about an area (Star and Estes, 1990).

Frederick Law Olmstead has long been considered the father of Landscape Architecture for his pioneering work in the early 20th century. Many of the methods Olmstead used in Landscape Architecture also involved the use of hand-drawn overlays. This type of analysis was beginning to be used for a much wider range of applications, such as change detection, urban planning, and resource management (Rado, 1992).

The first system to be called a GIS was the Canadian Geographic Information System, developed in 1962 by Roger Tomlinson of the Canada Land Inventory. Unlike earlier systems that were developed for a specific application, this system was designed to store digitized map data and land-based attributes in an easily accessible format for all of Canada. This system is still in operation today (Parent and Church, 1987).

In 1969, Ian McHarg’s influential work, Design with Nature, was published. This work on land suitability and land capability analysis (SCA), a system designed to analyze many data layers to produce a plan map, discussed the use of overlays of spatially referenced data layers for resource planning and management (Star and Estes, 1990).

The era of modern GIS really started in the 1970s, as analysts began to program computers to automate some of the manual processes. Software companies like Esri and ERDAS developed software packages that could input, display, and manipulate geographic data to create new layers of information. Steady advances in features and power of the hardware over the last ten years—and the decrease in hardware costs—have made GIS technology accessible to a wide range of users. The growth rate of the GIS industry in the last several years has exceeded even the most optimistic projections.

Today, a GIS is a unique system designed to input, store, retrieve, manipulate, and analyze layers of geographic data to produce interpretable information. A GIS should also be able to create reports and maps (Marble, 1990). The GIS database may include computer images, hardcopy maps, statistical data, or any other data that is needed in a study. Although the term GIS is commonly used to describe software packages, a true GIS includes knowledgeable staff, a training program, budgets, marketing, hardware, data, and software (Walker and Miller, 1990). GIS technology can be used in almost any geography-related discipline, from Landscape Architecture to natural resource management to transportation routing.

The central purpose of a GIS is to turn geographic data into useful information—the answers to real-life questions—questions such as:

  • How can we monitor the influence of global climatic changes on the Earth’s resources?
  • How should political districts be redrawn in a growing metropolitan area?
  • Where is the best place for a shopping center that is most convenient to shoppers and least harmful to the local ecology?
  • What areas should be protected to ensure the survival of endangered species?
  • How can communities be better prepared to face natural disasters, such as earthquakes, tornadoes, hurricanes, and floods?

Information vs. Data

Information, as opposed to data, is independently meaningful. It is relevant to a particular problem or question:

  • "The land cover at coordinate N875250, E757261 has a data file value 8," is data.
  • "Land cover with a value of 8 are on slopes too steep for development," is information.

You can input data into a GIS and output information. The information you wish to derive determines the type of data that must be input. For example, if you are looking for a suitable refuge for bald eagles, zip code data is probably not needed, while land cover data may be useful.

For this reason, the first step in any GIS project is usually an assessment of the scope and goals of the study. Once the project is defined, you can begin the process of building the database. Although software and data are commercially available, a custom database must be created for the particular project and study area. The database must be designed to meet the needs of the organization and objectives. ERDAS IMAGINE provides tools required to build and manipulate a GIS database.

Successful GIS implementation typically includes two major steps:

  • data input
  • analysis

Data input involves collecting the necessary data layers into a GIS database. In the analysis phase, these data layers are combined and manipulated in order to create new layers and to extract meaningful information from them. This chapter discusses these steps in detail.