The lay of the land

Patricia Cohen has an article in The New York Times about new mapping technology:

Few battles in history have been more scrutinized than Gettysburg’s three blood-soaked days in July of 1863, the turning point in the Civil War. Still, there were questions that all the diaries, official reports and correspondence couldn’t answer precisely. What, for example, could General Robert E. Lee actually see when he issued a series of fateful orders that turned the tide against the Confederate Army nearly 150 years ago?
Now historians have a new tool that can help. Advanced technology similar to Google Earth, MapQuest, and the GPS systems used in millions of cars has made it possible to recreate a vanished landscape. This new generation of digital maps has given rise to an academic field known as spatial humanities. Historians, literary theorists, archaeologists and others are using Geographic Information Systems— software that displays and analyzes information related to a physical location— to re-examine real and fictional places like the villages around Salem, Massachusetts at the time of the witch trials; the Dust Bowl region devastated during the Great Depression; and the Eastcheap taverns where Shakespeare’s Falstaff and Prince Hal caroused.
Like the crew on the starship Enterprise, humanists are exploring a new frontier of the scholarly universe: space. “Mapping spatial information reveals part of human history that otherwise we couldn’t possibly know,” said Anne Kelly Knowles, a geographer at Middlebury College in Vermont. “It enables you to see patterns and information that are literally invisible.” It adds layers of information to a map that can be added or taken off at will in various combinations; the same location can also be viewed back and forth over time at the click of a mouse.
Today visitors to Gettysburg can climb to the cupola of the Lutheran seminary, where Lee stationed himself on 2 July, the second day of fighting; or stand on Seminary Ridge, where the next day Lee watched from behind the Confederate lines as thousands of his men advanced across the open farmland to their deaths in the notorious Pickett’s Charge. But they won’t see what the general saw, because the intervening years have altered the topography. Over the decades a quarry, a reservoir, and different plants and trees have been added, and elevations have changed as a result of mechanical plowing and erosion.
Geographic Information Systems, known as GIS, allowed Knowles and her colleagues to recreate a digital version of the original Gettysburg battlefield from historical maps, documented descriptions of troop positions and scenery, and renderings of historic roads, fences, buildings, and vegetation. “The only way I knew how to answer the question,” about what Lee saw, Knowles said, “was to recreate the ground digitally using GIS and then ask the GIS program: What can you see from a certain position on the digital landscape, and what can you not see?” She said her work helps “make Lee’s dilemma more vivid and personal”. Nineteenth-century military leaders relied primarily on their own eyes, and small differences in elevation were strategically important. “Lee probably could not have possibly seen the massive federal forces building up on the eastern side of the battlefield on Day 2 during the famous attack on Little Round Top,” Knowles said. “He had to make decisions with really inadequate information.”
So did Lieutenant General James Longstreet, who was vilified in the Confederacy partly because of his decision on 2 July to take his troops on a long countermarch to avoid detection rather than attack Little Round Top directly. The march “made Longstreet the goat of Gettysburg,” Knowles said. But there was no way that Longstreet could have seen that Little Round Top was undefended at the time. “The analysis says Longstreet made the best decision he could,” added Knowles, who is currently working on a digital map of the Nazis’ territorial conquests and forced labor camps in Europe.
New methods of computer-assisted geographic analysis can also offer new interpretations of familiar topics. Geoff Cunfer, a historian at the University of Saskatchewan, revisited causes of the 1930s Dust Bowl by analyzing data from all 208 counties in Texas, New Mexico, Colorado, Oklahoma, and Kansas that were affected, an impossible undertaking without this system. He found that the traditional explanation of farmers’ extensively plowing the land without care for environmental limits was only true in some places. Barely plowed Southern counties also suffered from the plague of dust. Using reports of annual precipitation, unplowed grassland, wind direction, droughts, agricultural censuses, historical studies, and previous reports on dust storms— “a messy shoebox full of newspaper clippings”— Cunfer created data sets that could be plotted on maps. He discovered that dust storms regularly occurred in the nineteenth century and were a natural part of plains ecology before any plowing occurred, but were “unreported and unpublicized”, he said.
Advanced mapping tools, around since the 1960s, were initially used primarily for environmental analysis and urban planning. In the late 1980s and 1990s geographic historical information systems enabled scholars to take census information and other quantifiable data and plot changes in a location over time. By the late 1990s, professional networks and organizations began to form, but this sort of mapmaking remained on the margins.
This system insists on precision, explained David Bodenhamer, a historian at Indiana University who is editing a series of books on the spatial humanities. Every bit of data is represented by a point, a closed polygon or a pixel on a map. Critics complained this exactitude did not allow for multiple viewpoints. By the mid-2000s, technological developments enabled scholars to break out of the strict map format and add photographs and texts to create what Bodenhamer calls “deep maps,” which can capture more than one perspective. In 2005, Bodenhamer, collaborating with colleagues at Florida State University and West Virginia University, helped create the Polis Center in Indianapolis, which calls itself the first virtual spatial humanities center. One of their early projects was financed by the National Endowment for the Humanities: a detailed digital atlas of religion in North America that broke down denominations by county. Geographic Information Systems make it possible to analyze complex and changing patterns of political preferences, religious affiliation, migration, and cultural influence in fresh ways by linking them to geography, Bodenhamer said.
Benjamin Ray, the director of the Salem Witch Trials Documentary Archive at the University of Virginia, said visualizing data helps you analyze it. “The eye is a very good sorter of patterns,” he said. Ray had wondered why witchcraft charges spread so rapidly and widely in 1692 from Salem across 25 communities, whereas previous incidents had remained small and localized. When he plotted the accusations on a digital map that showed a progression over time, it struck him immediately: “It looked like a kind of epidemic, almost a disease.” That made him examine what the Salem authorities did differently this time that failed to contain the hysteria. He found that the judges broke their own rules by permitting people to make accusations without posting a monetary bond, letting accusers be interviewed in groups, and allowing “spectral evidence”— evidence only visible to the accuser— as sufficient for a conviction. After adding church affiliation to the map, he saw there was also a correlation between church membership and the accusers, which reflected a rift in the village over support for the minister.
Bodenhamer said the humanities had become too abstract and neglected physical space. The value of what scholars are calling “the spatial turn”, he added, is that “it allows you to ask new questions: why is it that something developed here and not somewhere else, what is it about the context of this place?”