New Mexico Geological Society Annual Spring Meeting — Abstracts

The use of personal computer systems with a graphical user interface make it possible to use existing CAD software to produce publication quality geologic maps directly from field data. Although any drawing program can be used to produce such maps, a program with a built in programming language (e.g. MiniCad+) allows the greatest flexibility and ease of use. The advantages of using MiniCad+ over other programs (e.g. Canvas) are the built in programming language (MiniPascal) and database at a comparatively low cost. The MiniPascal routines described here are primarily designed for structural mapping; routines can: easily be written/modified for other types of mapping.

The following is the procedure use to produce geologic maps with MiniCad+, and involve a number of MiniPascal routines specifically written for this purpose. The first step in producing any map is getting a suitable base map. If available, a digital base map can be imported (in DXF format from, for instance, a GIS system). Ifa digital base is not available, portions of the topographic map can be scanned (using a standard desktop scanner) and used as the base map. This scanned image is the lowermost layer of the map file, and is not normally printed. However, it is usually necessary to digitize some topographic data (e.g. roads, creeks, section lines) for geographic reference.

Geologic data is best added on a frequent basis (e.g. after each day in the field). MiniPascal routines were written to allow easy addition of geologic contacts (edge of outcrop, inferred, possible, defmite) and faults (thrust, normal etc.). These routines are accessed with a double click of the mouse, and each feature type is automatically placed on a different level. Station locations can be added, and the database associated with each station includes information like location, rock type, sample number, and extra notes. Structural data (e.g. S0, S1, L1 etc.) can, if needed, be associated with a station location. Again, routines are associated with each structural type, and you must enter the dip and dip direction,(or plunge and plunge direction). This data is stored in a database, associated with each symbol; other data which can be stored in the database include which way bedding is younging, foliation intensity, what features define the foliation (esp. for magmatic foliations). If an existing geological map is scanned, it is possible to select the end points of the structural symbol to calculate the strike at that location.

If a Powerbook is available, this can be taken to a base camp where the base map (the final map) can be updated on a daily basis. If a portable printer is added to the system, field maps can be printed for each days mapping, at whatever scale is appropriate. Maps can easily be changed to reflect new data, and updated geologic maps can be printed on a daily basis.

The database and MiniPascal allow MiniCad+ to be used as a simplified Geographic Information System (GIS). Both existing search criteria and MiniPascal routines can be used to access, display. and output specified data (provided this data has been input into the database). For instance you could access all data dipping greater than 45°, having a very strong magmatic foliation defined by feldspar phenocrysts. Structural domains can be defmed using the polygon tool. and data from the individual domains (i.e. within the polygon) can be exported to a text file which can be read by stereonet plotting programs.

Maps can be printed to any Mac supported printer (and joined to form the fmal map) or output to plotters (requires additional software). As each different geological feature is on a separate layer, the map can be output in DXF format, and imported into a GIS for compilation and production of a final map (e.g. Arc Info, the GIS the Bureau of Mines will be using to compile and produce geological maps in the future). Importing such digital maps into the GIS will decrease the possibility of subsequent digitizing errors, reduce the time required to check fmal maps, and shorten the time to get final maps into publication.