Program of the USGS in Texas Digital Geologic Atlas of Texas

Article taken from the USGS website http://tx.usgs.gov/GAT/index.html

The Texas Geologic Atlas Project was first cited in the University of Texas - Bureau of Economic Geology (BEG) Report for 1961. In September of that year, compilation of the first of 38 Geologic Atlas of Texas (GAT) hardcopy map sheets began. The project, under the direction of Dr. Virgil E. Barnes, involved the work of 28 BEG geologists and many other geologists, seven cartographers, and several editors. The last GAT sheet was published in 1987. The GAT has been on the BEG "Best Seller" list of publications for many years and can be found at: http://www.beg.utexas.edu/mainweb/publications/pubs-bstsell.htm
In October 2002, the USGS-Texas Water Science Center (USGS-TWSC), in cooperation with the Texas Natural Resources Information System (TNRIS), a division of the Texas Water Development Board, began development of an Environmental Systems Research Institute (ESRI) geodatabase model to capture the power of these data. Phase I (2002-2004) of this effort produced a library of 38 ESRI personal geodatabases representing the original 38 BEG map sheets. Phase II (2005-2006) involved the development of a Statewide Digital Geologic Atlas of Texas which combined the 38 personal geodatabases into one ESRI ArcSDE geodatabase containing more than 145,000 geologic features.

Phase I (2002 - 2004) Digital Conversion
The digital conversion of the original hardcopy map sheets began October, 2002. Project planning among the USGS-TWSC team established the need to utilize the personal geodatabase format for this procedure. This data format would allow for all the original map data (e.g. geologic time, formation descriptions) to be stored in a single database location with the geographic features.

The digital conversion included four main processing steps:
1. Pre-processing - All BEG map and scribe sheets were digitally scanned to TIFF format at 600 dpi.
2. Georeferencing - The scanned images were then georeferenced to a sheet-specific UTM projection using a network of 12 latitude/longitude locations. An Root Mean Square (RMS) error <0.004 was attained for each map sheet.
3. Editing - Using advanced geographic editing techniques; the raster linework was converted to vector polylines and polygons.
4. Attribution - The geologic features were then attributed directly from the original hardcopy maps.

Each geodatabase contains one feature dataset, named Geology250k. This feature dataset stores the geographic projection information for the geodatabase. Inside each feature dataset there are four feature classes: Rock Units, Member Polygons, Member Lines, and Faults. Each geodatabase also contains a georeferenced raster dataset of the original BEG hardcopy map sheet. Finally, the Look-up tables and relationships connect map information to spatial features.
Completed in September 2004, the results of this effort included:
• Library of 38 personal geodatabases representing each of the original BEG map sheets
• ESRI Style file used to symbolize all Rock Unit and Member formations identical to the original map sheets
• FGDC-compliant metadata for all geographic datasets
• QA/QC hardcopy documents delivered to cooperator for archival purposes

Phase II (2005 - 2006) Statewide Compilation

In May 2005, work began on completion of a statewide geologic dataset using the Digital Geologic Atlas of Texas library completed during Phase I of this effort. In order to accomplish this task we found it necessary to utilize the ArcSDE geodatabase model. This change in data format allowed for multiple-user editing, which increased production efficiency, and allowed for additional memory storage within the geodatabase. Completed in January 2006, the result of this effort was a statewide compilation of surficial geologic data housed in a single ArcSDE geodatabase containing:
• 117,000 RockUnit polygons
• 16,000 Member Formations (polygon and line)
• 11,000 Faults
• 554 unique geologic symbols for the Seamless dataset
• Various sheet unique geologic formations (Vents, Dikes, Collapse Structures, others)
 

 

Figure 1 Digital copy of the BEG source map for the San Antonio metropolitan area.	Figure 2 Digital Geologic Atlas of Texas data layers (RockUnits and Faults) overlain with TNRIS Basemap layers (Roads and Hydro).