Digital Historiography: Maps

• Jones, Christopher. Geographic Information Systems and Computer Cartography (Longman; 1997)
• Kraak, M.J. and Ormeling, F.J. Cartography: Visualization of Spatial Data (Longman; 1996) Hall, Stephen S. Mapping the Next Millennium (Vintage; 1992)

The use of maps in historical scholarship is not new. Readers of textbooks or monographs are not surprised to find maps used to supplement the narrative. One reason historians use maps is that they can convey spatial information more efficiently through maps than through the written word. Imagine trying to convey the spatial information found on a map of the Franco-Prussian War through words; such linguistic description is, of course, possible, but a map more clearly conveys the network-like relations between the bits of information. Although not as cartographically literate as geographers, most historians understand the value of maps to our work. Thus, when some historians use geographic information systems (GIS) to display or investigate the past, it might be tempting to view such digitized maps as fancier versions of a tried and true means of communication. Yet the potential implications of GIS for our work extend beyond the technical differences with tradition map making. The increased use of GIS by historians—which I endorse—could mean that the map, rather than being a secondary supplement, might become a primary medium of our thinking.

GIS is similar to, but not exactly the same as, a map on a screen. Indeed, GIS displays are very similar to maps in that they both represent information spatially, with the surface of the earth as the ultimate grounding for such information. However, to look at only the display function— like looking strictly at the display function of a traditional map—is to see only half of the capabilities of the technology. When teaching about the spread of Christianity, for example, I often use maps to help tell the story. I will first display a map transparency of the sea and overland trade routes of the Roman Empire, then I will show a transparency of the location of early Christian influence. Then, I physically superimpose the two maps to allow students to see relationships between trade and the urban foundations of early Christianity. GIS works on a similar principle. Using GIS, an historian can input data— even non-cartographic data—about population size, income distribution, voting behavior and the like; then, she can see relationships in this data, such as those between income and population clusters, or between voting and income. An important technical difference between the older method I described above and the newer methods made possible with GIS is that the initial data need not be spatial itself; however, the final product is displayed through cartographic form. Thus, while use of GIS would seemingly mean that one is just piling maps on top of one another, this layering allows for ease and efficiency of spatial analysis.

For those unacquainted with the technology, two texts provide a excellent introduction to GIS. Christopher Jones' Geographic Information Systems and Computer Cartography details both the storage and analytic functions of GIS. Written for undergraduate and postgraduate students, the text deals with the procedural techniques of data acquisition, storage of that data, and how the resulting display can be used for analysis. Additionally, the text deals with basic concepts of visual representation, concepts that may be familiar to geographers, but to which historians might need an introduction. Jones wrote this text with mathematicians, managers and scientists in mind; although he does briefly suggest that GIS can be applied to archeology, human geography and the social sciences generally, he does not deal with the way historians might apply the technology, although those applications will become clear to the imaginative historian after only a cursory glance at this text. Thus, it would seem that historians utilizing GIS are blazing trails not fully envisioned by scientists.

M.J. Kraak and F.J Ormeling's Cartography: Visualization of Spatial Data is very similar to Jones, except that the polarities have been reversed. While Jones writes mostly about GIS, and only secondarily about visualization, Kraak and Ormeling write primarily about visualization and mapping, with many references to GIS. Although not as useful as Jones as a practical guide, this text deals with more important issues. Historians accustomed to writing the results of their research understand the rules of verbal composition: syntax, grammar, word choice. Should historians wish to teach apprentices about the visual exploration of data, texts like Kraak and Ormeling—which deal with such visual conventions as graphing, symbolic representation and projections—might become as common as Strunk and White. Therefore, GIS reminds historians of the usefulness of the spatialization of historical information, and that such information is not inferior to ideas expressed through words. When working in a GIS environment, the map itself becomes the main vehicle of thought. Should historians continue to use GIS as a storage and analytic tool, should they display the results of their research through spatial mapping, then they might begin to view the visualization of data as a independent secondary source, not as merely a compliment to linguistic secondary sources. Although technically similar to a map, GIS has the potential to be deployed by visually- creative historians as a more consequential means of scholarly communication.

Is a visual display of information a "map" only if it makes reference to the surface of the earth? What if such a display does not make references to the earth? Is it still a "map?" Many scientists since the end of the 1940's have been using the visual capabilities of computers to explore relations in their data graphically and visually, much like users of GIS do. For example, mathematicians are mapping out pi in three dimensions; neurologists are mapping peptide receptors in the brain; cardiologists using digital subtraction angiography, CAT scans and magnetic resonance imaging (MRI) engage in a form of "anatomic cartography." For science writer Stephen S. Hall, these spatial displays are "maps," since he is willing to concede that the graphic representation of space need not be confined to the earth. "[The] narrow land-based definition of map, like the geocentric myth of the earth itself," he contends, "has been conceptually overwhelmed and ultimately retired"(5) because of the widespread use of computers by scientists. Another way of phrasing Hall would be to conclude that maps created via the visual capabilities of computers parallel the maps produced before Mercator: they are pictures of information not intended to mirror the earth's surface.

In theory, therefore, historians might use the computer to create visual displays of their information. Rather than producing a linguistic abstraction in the form of a monograph, historians might produce spatial abstractions, such as pictures of the boundaries between pre-industrial and industrial culture, or maps exploring changes in gender relationships, or any map that explores relationships in data visually, spatially and cartographically. Historians might begin to think like geographers—for generations, practitioners of our "sister discipline"—by analyzing data in cartographic, rather than linguistic, form. Visual secondary sources will not spring forth from the tool alone; only from historians who have the desire and imagination to use the mapping potential of the technology. Should historians reconsider the role of pictures in their work, the "map" would no longer be a prop, but would be the stage upon which we display our ideas about the past.