Spatial Thinking in Planning Practice: An Introduction to GIS

2 CHAPTER 1: DEFINING A GEOGRAPHIC INFORMATION SYSTEM Although GIS has been around since the 1970s, the concepts surrounding GIS are old, and even the practice of doing GIS began before computers. "e di#erence today is that GIS is computerized. By computerizing GIS, we have taken the processes away from our hand-drawn depictions, which tend to require extensive time, money, training, and energy. Computers process numbers and mathematical equations far quicker than people. Yet, before the concepts behind GIS were transferred to computers, people were doing manual GIS by combining spatial and attribute data on various types of media including hard-copy maps, hard-copy overlays (acetate or vellum), aerial photographs, written reports, !eld notebooks, and—of course—their eyes and minds. With manual GIS, a large base map was o$en 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. "is took time, and because of it, many great ideas about the relationships of the Earth’s features (both physical and human) were not analyzed. "ese ideas were constrained by the amount of time it took to do the analysis. Still, some impressive manual GIS projects did occur. "e much-repeated exam- ple of Dr. John Snow’s Cholera map is a great example of manual GIS (Figure 1.1). Figure 1.1. Dr. John Snow’s Cholera Map of London’s Soho. Source: Wikipedia http://en.wikipedia.org/wiki/ Geographic_information_system 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. "en, 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 clus- tered largely among those who lived near the Broad Street water well. He and his students took the handle o# 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.