GIS mapping is a powerful way to make history come to life. Combining geographic information system (GIS) data with historical information, may serve to:
- Present historical evidence in its precise geographical context,
- Visually convey geographic changes over time, or
- Tell engaging stories from a geohistorical perspective.
Visually illustrating change over time in this way is especially helpful when trying to convey complex information. Our historians frequently gather information that documents a range of activities that happened in a specific place over time. Describing our documentary findings in a traditional narrative may be cumbersome and can obscure important points. By linking this information to the relevant geographical features we “show” not just “tell” what happened where and when.
For example, we help lawyers involved in environmental cleanup cases to locate entities that once occupied a polluted site and quickly identify their likelihood of being a source of contamination. We have plotted the detailed information found in historical parcel descriptions onto current maps to help lawyers more easily see changes in boundaries, the relationships between parcels and owners, and timeframes when certain activities were documented on a site.
The process of GIS mapping is fairly straightforward, although not necessarily easy. It often starts with locating relevant GIS data from state or county government sources. This data might include information on roads, railroads, sewer lines, land/ lot parcels, waterways, or other elements. Historians then use GIS mapping software to add additional attributes and import them into the map — as long as the information is keyed to the same geographically referenced data. For historical maps, features can be “georeferenced” — or plotted with their specific coordinates — so that coastlines, roadways, and buildings are accurately layered over current maps. Other relevant information such as current or historical aerial photographs can also be layered in. Specific areas of interest can be highlighted by using stylistic options, such as shading or color coding. Layers can easily be turned on and off or adjusted for transparency in order to see how the landscape has changed over time.
Once we have embedded all the data, we can disseminate the information in a number of ways, from a simple graphic file, to a layered PDF, to interactive maps. Interactive maps allow the viewer to delve further into any additional data embedded in the map when a certain feature is selected. For instance, by clicking on a specific parcel, a popup window could display the parcel number, a photo of a factory that used to be on the site, a list of known residents at the location, operational descriptions excerpted from an historical document, and so on.
The main limitations to this type of work to date have been the quality of GIS data available for a specific region, and the availability of digitized, high-resolution historical maps. The good news is that both of these data sets are becoming more widely available. The U.S. government has launched a web portal designed to foster information sharing and provide access to geospatial data and services. Major map digitizing projects are also underway to preserve older maps and to make them more widely available. Since 1995, the Library of Congress has been digitizing its massive collection of over 5.6 million maps, atlases, and other cartographic materials. A small but growing portion of this material has been converted to digital format and is available online. Similarly, the New York Public Library has scanned nearly 9,000 maps in its map collections and has begun working to index the collections to Google Earth. Similar projects are happening worldwide.
Although availability of GIS data and intuitive software will make it easier to create GIS-based presentations, just having the tools will not automatically make the map any easier to understand. The contextual knowledge and interpretative skills of the trained historian are essential in producing cartographic presentations that are not only accurate, but convey the information so it is properly interpreted.
At History Associates, we have used GIS mapping to help visualize the evolution and ownership of large industrial sites, to show moving battle lines for several theaters of war in World War II, and to illustrate how changes in and along a waterway related to historic land use. As the technology improves, we continue to discover new ways to use this powerful tool to help others not just conceptualize, but see the events that happened in one specific place over time.