THE USE OF REMOTE SENSING TO VERIFY THE ACCURACY OF DIGITIZED SURFACE GEOLOGY MAPS

There are two methods that can be used in the conversion of a paper geologic map to a GIS database. The first process involves the use of a digitizer tablet and a person to physically record, by the use of a “puck,” each feature on the paper map. The second method takes the best available representation of the hardcopy map and, using a large-format scanner, converts the map to a digital image. The digital image is georeferenced to a coordinate system based on location information from the published map. If the map is based on a USGS topographic map, then the corners of the map can serve as four of the necessary control points. The digital geologic database takes shape by tracing the features on the scan image. Ideally the new geologic database will accurately overlay a scanned image of the topographic basemap used in the creation of the original geologic map. However, due to errors in the original cartographic and digital conversion processes there can be significant errors in the new database. Therefore, an effective method is required to examine the accuracy of maps created in the manner described above.

The use of remote sensing techniques offers such a method. A LANDSAT image, with the “normal” TM band combination of 1-2-3 for R-G-B, can be used a backdrop to the geologic line work where it can be compared to see if there is a correlation. The RGB combination of 742 can be used to highlight significant geologic features. Edge detection methods can also enhance the boundaries between units. In addition, it is possible to reclassify a LANDSAT TM image to divide out the different mapping units. This presentation demonstrates the use of LANDSAT remote sensing techniques and describes the steps taken to verify the GIS database for the NMBMMR Geologic Map 57.