USGS digital elevation models are produced from models based on aerial photographs and satellite remote sensing images. The USGS 7.5 minute DEM data are georeferenced using the Universal Transverse Mercator (UTM) coordinate system. For this study, the DEMs used were developed by the USGS and distributed by the Texas Natural Resources Information System (TNRIS). The USGS is also producing a 10 meter DEM; however the regional availability of these elevation models is less than that of the 30 meter DEMs.
ArcView GIS 3.2 and CRWR-PrePro
Case III explores using ArcView GIS 3.2 and CRWR-PrePro to delineate the watersheds using two different spatial resolutions. As mentioned previously, this part of the study entails using two different resolution grid DEMs: a 10 meter DEM and a 30 meter DEM. All data are projected into the TCMS Albers Equal Area georeferencing system. The Texas Geographic Information Council (TGIC) defines a statewide mapping system for use in projected geospatial datasets that cover Texas in order to facilitate overlay and integration of datasets. The Texas Centric Mapping System/ Albers Equal Area or TCMS/AEA is defined below:
Mapping System Name: Texas Centric Mapping System/Albers Equal Area
Mapping System Abbreviation: TCMS/AEA
Projection: Albers Equal Area Conic
Longitude of Origin: 100 degrees West (-100)
Latitude of Origin: 18 degrees North (18)