1.3: Manual Gis And Computer-Based GIS

Abler’s and DeMers’ quotes may give you the impression that GIS is a new concept. Although the term GIS has been around for more than 30 years, the concepts surrounding GIS are old, and even the practice of doing GIS began before computers. The difference today is that GIS is computerized, but there is nothing a computer can do that cannot be done, at least theoretically, by hand if you had enough time, money, and energy. Computers process numbers and mathematical equations far quicker and more accurately than people can by hand or with the use of a calculator. Yet, before the concepts behind GIS were transferred to computers, people were doing manual GIS. They just combined spatial and attribute data on various types of media including hard-copy maps, hard-copy overlays (acetate or vellum), aerial photographs, written reports, field notebooks, and—of course—their eyes and minds.

With manual GIS, a large base map was often placed on a tabletop, and a series of transparent overlay maps, drawn at the same scale, were placed on top of the base map. One would then look for relationships among the base map and the features on the transparent overlays. Frequently, spatial data were copied from one map (or aerial photograph) to another. This took time, and because of it, many great ideas about the relationships of the Earth’s features (both physical and human) were not analyzed. These ideas were constrained by the amount of time it took to do the analysis. Still, some impressive manual GIS projects did occur.

The much-repeated example of Dr. John Snow’s Cholera map is a great example of manual GIS. In the 1840s, a cholera outbreak killed several hundred residents in London’s Soho section. Snow, a physician, located the address of each fatality on a hand-drawn base map and soon a cluster of cases was visible (Figure 1.3).

Figure 1.3: Dr. John Snow's Cholera Map of London's Soho.

Then on the base map, over the streets and fatalities, he drew the locations of water wells. Familiar with the idea of distance decay, he knew that people might go a far distance to purchase a product that was cheaper, but they would go to the nearest well because water was free and heavy to carry. Snow could see that the fatalities clustered largely among those who lived near the Broad Street water well. He and his students took the handle off the water pump, and new cholera cases dropped rapidly. By disabling the pump, Snow demonstrated the spatial relationship between cholera fatalities and the Broad Street water well, and, more importantly, he established the relationship between cholera and drinking water.

Even with the advent of computers, it took decades for GIS applications to get to where they are today. The largest and most powerful computers were mainframes that were available to some academics and government officials, but not to many researchers. In the 1980s, most GIS applications ran on workstation computers tied to mainframe computers because the early microcomputers (IBM, Apple, etc.) did not have enough memory, storage capacity, or processing ability. Today’s personal computers, however, are fast, capable of storing and processing large datasets, and can process multiple tasks simultaneously. This enables many academics, government agencies (from local to federal), organizations, and small and large businesses to use GIS. Computer-based GIS has its advantages, but requires educated users.