The Geologic Data Subcommittee (GDS) of the Federal Geographic Data Committee (FGDC) is responsible for coordination of geologic data-related activities

FGDC Digital Cartographic Standard for
Geologic Map Symbolization

Guidance on how to use the Standard:

General -- This standard is not intended to be used inflexibly or in a manner that will limit one's ability to communicate the observations and interpretations gained from geologic mapping. On the contrary, we recognize that, in certain situations, a symbol or its usage might need to be modified in order to better represent a particular feature on a geologic map or cross section. To that end, we emphasize that this standard allows the use of any symbol that doesn't conflict with others in the standard, provided that it is clearly explained on the map and in the database. In addition, modifying the size, color, and (or) lineweight of an existing symbol to suit the needs of a particular map or output device also is permitted, provided that the modified symbol's appearance is not too similar to another symbol on the map. Be aware, however, that reducing lineweights below .125 mm (.005 inch) may cause symbols to plot incorrectly if output at higher resolutions (1800 dpi or higher). For more information, please refer to the Standard's Introductory text, specifically Section 7. "Technical Specifications Used in the Preparation of this Standard". To facilitate the use of this standard, we include in the Preface to Appendix A tables showing conversion values from inches to points to millimeters (Table 1), abbreviations used (Table 2), and spot color specifications and their equivalent colors in other color models (Table 3).

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