Urban planners, and transportation planners in particular, have tested all sorts of techniques for modeling how people move through cities. These maps of greater Chicago, with their starbursts of white lines etched against a dark background, exemplify how early computer cartography was seen as a promising technique for processing this kind of data. The maps trace “desire lines”—defined in the study as “the shortest line between origin and destination”—among origin and destination points for three different modes of transportation: the subway-elevated rapid transit system (Figure 18), public buses (Figure 20), and automobiles (Figure 22). Acknowledging that “the desire line is, of course, unrealistic,” the study’s authors insisted that it remained a “simple and completely unbiased presentation” of the location and magnitude of travel in Chicago. Because these maps would go on to inform urban planning decisions, the desire lines are models of the future just as much as they are maps of the present.
There is an order in human travel behavior in urban areas which can be measured and described. This order provides the basis for intelligent forecasting which is necessary so that solutions will cope with the problems of the future—not just those of the present or past.
The machine displayed in Figure 52—the “Cartographatron”—processed and printed the Transportation Study’s desire line maps. It processed a staggering dataset of over 10 million “person trips” that were manually gathered and recorded through more than 58,000 surveys and interviews; stored on approximately 378,000 punched cards; and eventually, transferred to nineteen reels of magnetic tape. This included each trip’s 22 attributes, such as length, purpose, time of arrival, land use, zone of origin, direction, mode of travel, and more.
Origins and destinations for each trip were geographically associated with sections of a quarter square mile grid overlaid on the study region. Then, the Cartographatron read the magnetic tape, translated the numerical values stored on it into voltages, and used those voltages to generate a spot of light that moved across the face of a cathode ray tube. The path of the “blip,” as the study authors called it, was recorded on a photographic plate, with “the weight of each line being directly related to the speed of the moving blip.”