chapter one Historical Maps in GIS David Rumsey and Meredith Williams ost historical GIS would be and scientifi c understanding at the time of impossible without historical its creation. By incorporating information M maps, as the chapters in this book from historical maps, scholars doing his- testify. Maps record the geographical infor- torical GIS are stimulating new interest in mation that is fundamental to reconstruct- these rich sources that have much to offer ing past places, whether town, region, or historical scholarship and teaching. At the nation. Historical maps often hold informa- same time, the maps themselves challenge tion retained by no other written source, GIS users to understand the geographic such as place-names, boundaries, and physi- principles of cartography, particularly scale cal features that have been modifi ed or and projection. We have addressed these erased by modern development. Historical challenges in order to examine the value of maps capture the attitudes of those who including nineteenth- and early twentieth- made them and represent worldviews of century paper maps in GIS.1 their time. A map’s degree of accuracy tells One can use digital renditions of histori- us much about the state of technology cal maps to study historical landscapes, the ch01 1 1/3/03, 11:21:23 AM 2 past time, past place: gis for history Figure 1. Wheeler Survey map of maps themselves, and how places changed were only as reliable as the reader’s visual Yosemite Valley, 1883 over time. GIS is breathing new life into acuity and interpretive skill. The same The government-funded Wheeler historical maps by freeing them from the limits applied to cartography, the making Survey produced one of the fi rst accu- static confi nes of their original print form. of maps. Cartographers traditionally made rate maps of Yosemite Valley. The It is also enabling a new level of understand- maps by gathering information from pub- cartographers who drew the map ing. Traditionally, people read and analyzed lished maps or fi eld surveys. The maps used hachuring (a form of shading) maps using a critical eye and a priori they produced were often marvelous acts to suggest the depth of the canyon knowledge. Comparison of two or more of interpretation. Consider the Wheeler and the river valleys leading to it. maps was possible, but the conclusions Survey, which mapped territory west of ch01 2 1/3/03, 11:21:26 AM Chapter 1 Historical Maps in GIS 3 the 100th meridian in a series of geo- in a continuous landscape were as much graphical expeditions beginning in 1871. art as science (fi gure 1). When their map George M. Wheeler and his associates car- is converted into digital form, it can be ried heavy plane tables, surveyor’s instru- manipulated and combined with other spa- ments, and large-format cameras by wagon tial data, such as digital elevation models and mule across mountains, canyons, and (fi gure 2). The three-dimensional landscape deserts. Their survey points were highly is more immediately recognizable. It gives accurate for the time, but the renderings us the feel of standing next to the cartog- of the topography that linked those points rapher as he gazed over Yosemite Valley. Figure 2. Wheeler’s Yosemite Valley in 3-d Draping the scanned image of the original Yosemite map over modern digital elevation model maps gives the old map a new look and immediacy. The simulated depth of the 3-d terrain model complements the beautiful hachuring of the 1883 map. In this map we used a vertical exaggeration factor of 1.5. ch01 3 1/3/03, 11:21:52 AM 4 past time, past place: gis for history More importantly for the aims of histori- graphic images. Connected by hot links to cal research, information that was diffi cult particular features in a GIS layer, histori- Figure 3. Chicago in 1868 to perceive in the historical map is now cal maps can be opened to compare pres- and 1997 accessible for our own investigation. We ent and past confi gurations of a given place Hot links connecting historical can now measure elevation, distance, and or landscape (fi gure 3). city plans to present-day maps give area, and rotate the image to place our- Integrating historical maps in GIS students easy access to visual com- selves at different viewpoints. to analyze the spatial information they parisons. Rufus Blanchard’s Guide Ordinarily, the fi rst step in preparing contain, or to layer them with other Map of Chicago (1868) shows the a paper map for use in GIS is scanning spatial data, requires that the maps be city’s characteristic grid and cross- it. For this purpose, it is best to capture georeferenced. That is, selected control cutting diagonal arteries, little map images at a very high resolution.2 points on a scan of the original map must changed in a recent ArcView® If one’s main purpose is to study maps as be aligned with their actual geographical StreetMapTM. The dimensions of historical documents, scanning may be all location, either by assigning geographical the city, however, have changed the manipulation required. Scanned maps coordinates to each point, or by linking enormously. can be easily incorporated into a GIS as each point to its equivalent on a modern, ch01 4 1/3/03, 11:22:12 AM Chapter 1 Historical Maps in GIS 5 accurate digital map. Once the control Jesuit missions.3 Placing the missions in Figure 4. Adding features to a points are in place, one applies mathemati- their physical context helps one see the historical map cal algorithms to warp the original map geographical logic of their location and This 1882 georeferenced map from image to fi t the chosen map projection as infer their relationship with regional pat- the Wheeler Survey shows the nearly as possible. Further adjustments can terns of commerce and transportation that Rio Grande Valley just north be done manually to try to fi nd the best developed between their founding in the of Santa Fe. The cartographer’s fi t for all parts of the original map. The late seventeenth century and their decline hachures mark the steep plateaus process is sometimes called rubber sheeting at the end of the nineteenth. and mesas of the rugged region because it stretches and shrinks the map It is almost impossible to perfectly align where Franciscan priests established image like a thin sheet of rubber being an old map to modern coordinate systems missions among the native Indian pulled to fi t a particular form. Figure 4, because mapping methods before the age people as early as 1692. The red points for example, is a scanned detail of the of aerial photography often only very represent a layer of database informa- Wheeler Survey’s 1882 map of New Mexico imprecisely represented scale, angle, dis- tion about the missions. By click- that we georeferenced and then layered tance, and direction. For most GIS proj- ing on the points, users can bring with point data marking the location of ects, the value of the historical information up historical data about each site. ch01 5 1/3/03, 11:22:33 AM 6 past time, past place: gis for history on paper maps more than compensates for those for longitude converge. A common the residual error in their georeferenced conic projection for maps of the continen- versions. What one should keep in mind tal United States is Albers Equal-Area, so is that georeferencing does not necessarily we used a vector layer in this projection as improve a historical map or make it more a base for georeferencing the exploration accurate. In the course of changing the map. Control points were taken by assign- original map to make it amenable to digital ing geographical coordinates to reference integration, georeferencing changes lines points, such as the explorer’s longitude and shapes, the distance between objects, and latitude marks and major river junc- the map’s aesthetics, and its value as a cul- tions. By then overlaying modern high- tural artifact. One gains knowledge of the ways (red) and state boundaries (brown), original while processing it for inclusion in one can gauge Lewis and Clark’s errors in GIS, but one also loses something if the measurement and estimation. original map is not represented for compari- Small-scale historical maps like Lewis son with its actual size, proportions, and and Clark’s are prone to greater error qualities. Ideally, researchers should include than large-scale maps.4 A large area of the both the warped map and the scanned earth’s surface, like the continental United image of the original map in a GIS project States, is harder to depict on a fl at surface or publication. than a small area such as a town.5 Large- The impossibility of aligning historical scale maps are often more easily and accu- maps perfectly with modern maps can rately converted for use in GIS because itself yield historical information. During they tend to have less egregious geographi- their exploration of the Louisiana Pur- cal errors. Maps drawn at a large scale may chase, Meriwether Lewis and William also have more unique local data to con- Clark made notations of longitude and tribute, such as information on land own- latitude, which they later used in drawing ership, the location of buildings, paths, the monumental map of their expedition and streams, and so forth. (fi gure 5). To bring this map into GIS, we Large-scale city maps can be wonderful began by estimating the projection used sources for urban history, and adding one for Lewis and Clark’s rendering.