New Mexico Geological Society Annual Spring Meeting — Abstracts

This project involved the conversion of NMBM&MR Geologic Map 53: Geology of northwest part of Las Cruces 1 ° x 2° Sheet, New Mexico (Seager et al. 1982) into digital form using GIS technology. The majority of this process was completed using the Arc/Info program with some of the final attribute editing performed in Arc/View. There were several steps involved in completing this project. The initial step was to load the published map into the computer as a warp grid. This was done by scanning a scribe sheet supplied by the NMBM&MR. Using this grid as a backdrop, a GIS coverage was created by tracing the grid on the computer using Arc/lnfo. This method is called "Heads Up Digitizing" and tends to be more precise than digitizing a hard copy of the original map. Two separate coverages were created to contain the line work. The first coverage contains the lines that form the boundaries for the geologic units represented by polygons on the map. The second coverage contains the line work for the geologic structure represented on the map, ie. Faults, Folds, etc. Once these coverages were completed, and all of the arcs were attributed, topology was built for the "geologic unit" coverage so that polygons could be produced and attributed. This portion of the work was done using the Arc/View program. Within the polygon edit feature a Name field was reated, which contains a name for each polygon that corresponds with the geologic unit it represents. A Symbol field was also used containing values from a constructed shade set which assigned each polygon a color, and texture where necessary. These shades were created to correspond with the shades represented on the original map. Upon completion of the edits, this map and its description can be printed out at a scale of 1: 125,000 or can be modified to fit the specific needs of a project. However, this GIS database should be used in conjunction with the published GM-53. This geologic database is in Arc/Info export format and has FGDC metadata.