National Geologic Map Database

To create, manage, and disseminate digital earth-science information, it is increasingly clear to data producers and users that certain widely-accepted standards are essential. In the past, many organizational units (e.g., projects or programs) have of necessity developed their own standard practices for creating and managing digital map data. Because the resources needed to develop widely-accepted standards are difficult for a single organizational unit to justify, many of these standard practices developed in an ad hoc fashion, with scant input from other groups.

Two notable mechanisms now exist in the United States to promote the coordination of widely-accepted standards: 1) the National Geologic Mapping Act of 1992 stipulates that necessary standards be developed by USGS and the Association of American State Geologists (AASG) to support the National Geologic Map Database (NGMDB); and 2) the Federal Geographic Data Committee (FGDC), through its Geologic Data Subcommittee, is responsible for development of standards to support geologic data management at the Federal level.

The links below contain information pertinent to the development of standards and guidelines for geologic mapping. Many of these works stemmed from discussions held at the annual Digital Mapping Techniques workshop, sponsored by the NGMDB and the Association of American State Geologists. The beginning stages of this work (ca. 1996-1997) are documented and preserved in an archival site and in the earliest NGMDB reports of progress.

"GeMS" — standard Geologic Map Schema

"GeMS" (formerly named NCGMP09) is the standard schema for geologic maps funded by the USGS National Cooperative Geologic Mapping Program (NCGMP). Its design specifies encoding the content analagous to that contained in a single, traditional geologic map. GeMS is intended to provide a stepping stone toward development of multimap databases, in particular the National Geologic Map Database (NGMDB). Please visit our GeMS site.

Related, Older Database Designs

This list focuses on the work by USGS and AASG staff, ca. 1998-2010, to define conceptual data models and physical implementations, mostly preceding development of NCGMP09.

Additional Resources

FGDC Cartography Standards

The National Standard for the digital cartographic representation of geologic map features.

Additional Resources


The NGMDB requires that metadata for submitted geologic geospatial data are in the FGDC Content Standard for Digital Spatial Metadata (CSDGM)

Geologic Time Scales

At the Geolex site, we provide some information and links to selected time scales. It's always advisable to cite in your publication the time scale you're using.

Science Terminologies

Many classifications have been devised in attempts to organize and standardize descriptions of geologic map units, both to improve science and to more clearly convey geologic information to the public. Of necessity, such classifications are compromises that only partially describe the near-infinity of map-unit compositions, textures, genesis, and appearance. In this section, selected terminologies developed by USGS and AASG in support of joint efforts to devise a common database design are highlighted. The reader also is encouraged to consult the vast body of published literature on this subject.

Base Maps and Projections

Topographic and cultural information are essential to a well-constructed geologic map. This section provides some links on major topics, including map projections.

Tools and Techniques

A few handy coordinate-conversion utilities and other resources are provided below. Suggestions for additional links are welcome.

Publication Guidelines for Geologic Maps