Texas Geology for GIS (ArcGIS *.shp files)

So, I am finally getting back to GIS. This may be a more technical (for the average Joe) post than usual – again I’m thinking about spawning a GIS blog…

I’ve switched from AutoCAD to ArcGIS for my geotech report drawings such as site (vicinity) maps and boring plans. Getting the geographic information such as roads, streams, lakes, counties, towns as ArcGIS-ready shape files hasn’t been that difficult. For coverage of North Central Texas, there is the NCTCOG (North Central Texas Council of Governments) GIS website. Once you have the basics, you can start creating great maps.

But I’ve had a hard time finding geology data. I started with *.SID files of the Geologic Atlas of Texas (GAT), such as the Dallas Sheet covering the Metroplex. I dont’ remember where I found these files but I downloaded about 1GB of maps… these files are basically raster images that are ‘adjusted’ (distorted) to fit geographic maps. Basically you can use them as overlay for any other themes you want to show on your maps. But the files are images, and therefore not as useful as shape files. Once you start blowing up things, you very quickly get into porr-resolution territory, and then the SID images become useless.

What I needed were shape files where the geologic information is vectorized. At TNRIS (Texas Natural Resource Information System), you can buy shape file info for the entire state at $56. I was going to do so but had forgotten where I had seen this offer. Then, I stumbled across this page on the USGS (US Geological Survey) website that offers shape file coverage for the entire state ‘apparently’ for free – in one 103 MB file. Awesome ! Now, I can create geological site vicinity maps at a click of a button, and won’t have to scan the paper sheets anymore.

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