Geospatial

On the Map

The Texas Historic Overlay sheds new light on Texas.

by / November 27, 2007 0
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,

the real map quest began. Brown's team began searching through archives in the state as well as the U.S. Geological Survey in Denver and the National Archives in Washington, D.C. These archives yielded more than 1,000 usable maps and detailed long forgotten sites of historical significance.

Historians on Brown's team discovered thousands more maps by scouring the small, local repositories within the state. When all the map hunting was completed, the team had collected more than 3,000 maps, some of which dated back 300 years.

As an added benefit, Brown said they were able to help local repositories get a better grasp on the vast amount of data they had stored.

"A lot of the smaller repositories, particularly in Texas, didn't have a complete inventory of their maps," he explained. "When our historians went in there, they actually left with a complete inventory of what they had and turned that over to the various repositories. That was a big plus for them."

 

Map Capture
The next challenge was digitizing the more than 3,000 maps. Even if all the maps were brand new, this would still be a significant undertaking. But with 300-year-old maps, one can't simply slap them into a scanner - extreme care must be taken so the brittle, old paper doesn't disintegrate.

"With some of these old maps, we were very apprehensive, even in clear Mylar sleeves, putting these things through scanners," Brown said.

Fortunately PBS&J had a subcontractor in the University of North Texas (UNT). And it just so happens that UNT possesses a Better Light Super 8K camera - an extremely high-end scanning camera that can produce images of 12,000 x 15,990 pixels and up to 1.1 gigabytes of resolution - meaning the camera can take pictures that are more than 100 times as detailed as a top-of-the-line 10-megapixel camera familiar to consumers.

An agreement was struck between UNT and PBS&J to use the camera to digitize the collected maps. To provide as much protection for the older maps as possible, UNT employed a vacuum easel, which uses suction to hold delicate documents flat and in place so the camera can do its work.

"[UNT's] process was to take this vacuum easel, lay the document on there; it would hold the document straight and vertical," Brown said. Once in position, he said, they could take an extremely high-resolution images. "They would take a snapshot of it. It would be to scale, and the image quality we got from that process was so high that we completely cut out scanning."

Making the enormous job a bit easier was the fact that UNT's camera was mobile, meaning PBS&J could bring it onsite instead of transporting the maps from their repositories.

After digitizing the thousands of maps - be they land surveys, bird's-eye views, and hand-drawn maps - Brown and his team put the data into a statewide geodatabase. Now, TxDOT can access these maps and use the data to better prepare construction plans designing highways around critical sites instead of over or through them.

"It's giving us a lot of value," Abbott said. "We're really quite happy with the feedback we've been getting and our ability to identify potential problems or resources out on the landscape."

Additionally Abbot said the Texas Historic Overlay provides state historians with unprecedented access to Texas' past.

"We've gotten feedback from ... our historical consultants who say this is just a wonderful thing that has saved them so much time because we've been able to gather these resources which have heretofore been scattered all over the state and were not being used, and bring them into one place where they are readily accessible."

In Texas, the storied, romantic and sometimes brutal past was recorded, at least in part, by cartographers from centuries past. But now, it seems, the history of much of the wild, wild West has finally been tamed.

Chad Vander Veen

Chad Vander Veen is the former editor of FutureStructure.