TxDOT Maps Texas History Information for planning transportation and other projects By Ty Summerville, Geospatial Project Manager, PBS&J Texas Department of Transportation (TxDOT) created a GIS-based historic archaeological resource that helps avoid sensitive archaeological and cultural sites and guide field surveys. From the long-lost missions built during Spanish rule to the historic cattle drives along the Chisholm Trail, Texas geography tells a varied and diverse story that historians, archaeologists, and cultural resource experts are still trying to write. It's up to agencies like TxDOT to ensure history is preserved while keeping the current residents moving forward. Second in the nation in both size and population, Texas is home to 23 million people, and cars and trucks are the primary mode of transportation. Currently TxDOT maintains the public highways that crisscross the state's almost 270,000 square mile area. By 2020, road and rail freight moving to, from, and within Texas is expected to increase by 70 percent, while population is expected to increase 52 percent by 2030. In an effort to more effectively manage cultural resources affected by highway construction and maintenance, archaeologists and historians in TxDOT's Environmental Affairs Division teamed with PBS&J to create a GIS-based historic archaeological resource. The Texas Historic Overlay (THO) would provide important information needed for planning transportation improvements and maintenance projects. The source information for creating the GIS would be historic-era maps. Today, the THO is an integral part of TxDOT's efforts to preserve and protect valuable resources, along with almost 80,000 miles of state highways, while securing rights-of-way for highway widening and new alignments for the future. Historic Map Collection The THO project began with an effort to gather out-of-print historic maps with significant cultural detail that were created between 1722 and 1988. The effort focused on the eastern half of Texas, an area that comprises 62 counties covering 145,000 square miles. More than 3,000 historic maps exist for this area. Over a two-year period, the THO team solicited information from 162 libraries, museums, The THO project gathered out-of-print historic maps with significant cultural detail such as this map of Dallas, Texas. and repositories. Once the information was gathered, the team scanned, processed, georeferenced, and indexed these maps and incorporated them into a single system. Maps were supplied in a variety of formats including scanned hard copies, photographic reprints, microfilm, digital photography, and tracings of hard-copy maps on vellum. The map images were initially enhanced in Adobe Photoshop to adjust brightness and contrast, replace aged paper color with white, and remove any blemishes present on the maps. Bibliographic and other detailed information regarding source maps was captured in a Microsoft SQL Server database. 20 ArcUser Summer 2009 www.esri.com