On the Map

As many Texans are aware, the Lone Star State is a veritable treasure trove of history. Once possessed by American Indians, Texas would eventually come under the rule of Spain, followed by Mexico, then move toward independence and self-rule, finally being annexed by the United States in 1845. A mere 16 years later, however, the new state would secede from the Union to join the Confederacy in 1861. Following the end of the Civil War, Texas was again granted admittance to the Union in 1870.

From the Comanches and the Tonkawas to Sam Houston and General Santa Anna, Texas has been the site of a fascinating and diverse array of people and cultures. As such, strewn throughout the state are countless relics, artifacts and geographic sites of significant interest. As the state continues to grow and expand its infrastructure, it has taken a unique step to ensure that its past is not paved over by modern development.

Roads and highways are, of course, among the most common and most invasive part of any infrastructure, stretching well past city limits and out in the vast, untamed expanses that claim much of the American Southwest. The Texas Department of Transportation (TxDOT) knows this and wanted to find a way to preserve and protect the state's history as it continues to build badly needed roads. Thanks to an innovative mapping project called the Texas Historic Overlay, TxDOT can now easily pinpoint thousands of historically significant sites, allowing the agency to design highways that will have minimal impact.

Map Quest
What makes the Texas Historic Overlay project interesting is that it tackles a complicated problem in an innovative fashion. The problem is that, as one goes farther back through history, records are less accurate, less detailed and less common. So how is an agency like TxDOT supposed to find sites of historic significance before they start digging? The answer: maps, lots and lots of maps.

The transportation agency brought in PBS&J, a nationwide engineering firm, to design an application that would incorporate the data from thousands of maps into a database where it could then be overlaid onto highway and road construction plans.

"Our idea was we would hire a contractor to go out and locate historic maps that had information about where there may be historic archaeological sites for planning purposes and to take those maps, put them on a digitizing table, identify resources on there and digitize those resources so they would show up in a GIS layer," said Jim Abbott, staff geoarchaeologist at TxDOT's Environmental Affairs Division.

Thomas Brown, a PBS&J engineer, led the team that built the Texas Historic Overlay. The biggest challenge, Brown said, was gathering thousands of maps - many of which were more than 100 years old - and organizing the data they contained into a coherent structure.

"What [TxDOT was] finding is there was not a centralized, complete collection of historical maps - gravesites, historical buildings, historical structures, things that are maybe not shown on current maps, old historic trails that were used by the Native Americans, cultural resources like that. They found they would go to the same repository once or twice and a map might be checked out or might not be available. So even finding the same map again sometimes was proving to be problematic."

Brown's team initiated a pilot project in Harris County to show a basic proof of concept. The idea was that the team could go to repositories both in Texas and in national archives and collect all kinds of maps. Once collected, the maps can be geographically referenced using GIS software from ESRI.

Upon seeing the results of the pilot, TxDOT asked PBS&J to expand map collection to include more than 100 counties. When that order came through,