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National Cooperative Geologic Mapping Program

WHAT IS A GEOLOGIC MAP?

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Geologic Map Databases

The main goal in many geological surveys no longer is to create a single geologic map but to create a database from which many types of geologic and engineering geology maps can be derived. This requires a database design or "data model" that is sufficiently robust to manage complex geologic concepts such as three dimensional (spatial) and temporal relations among map units, faults, and other features (fig. 2).

This is especially challenging because the software that manages these databases is not static but continues to evolve, thereby requiring an adaptable database design. Also, to permit the exchange of databases among agencies and users, either a common database design or a common interchange format is required. These design efforts are underway in North America and other parts of the world. As a consequence, geologists now are reevaluating how information is managed in the field, what kind of information is gathered and for what purpose, and the extent to which map information, once it has been created, can be updated to include new observations and interpretations.

Fig. 2. Three-dimensional stack of glacial geologic layers in east-central Illinois.

Figure 2. Three-dimensional stack of glacial geologic layers in east-central Illinois. Layer 1 (top) is land surface; layer 8 (bottom) is the underlying bedrock. The light-colored unit in layer 7 is a sand and gravel aquifer filling a bedrock valley, and buried by low-permeability glacial till. After Soller, D.R., et al., 1999, Three-dimensional geologic maps of Quaternary sediments in East-Central Illinois, U.S. Geological Survey Geologic Investigation Series Map I-2669, 1:500,000-scale.

Traditionally, once the geologist delivered a manuscript map to the cartographer, the job was finished. Map databases are meant to be maintained, and so a map can now be more accurately considered a progress report that can be updated. A critical aspect of the map database is the ability to manage the information and to preserve its integrity, for example, by migrating it to a new data format or structure or to a new standard terminology.

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Related Information

Meeting Challenges with Geologic Maps
(8.1 Mb Adobe® PDF)

Overview of Geologic Maps

Geologic Mapping:
AASG Position Paper (1.9 Mb Adobe® PDF)

Hazards:
AASG Position Paper (1.3 Mb Adobe® PDF)

The Value of Geologic Mapping:
Geological Society of America Position Statement

Tapestry of Time and Terrain

Geologic Map of North America

Digital Mapping Techniques Proceedings

Geographic Information Systems


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