Geologic Mapping
Milt Wiltse

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Over the past decade, the practice of generating geologic maps has been undergoing an accelerated evolution as Geographic Information System (GIS) and information technology (IT) capabilities are used to help derive geologic guidance for many environmental and economic problems. The acceptance of GIS as a fundamental geologic mapping technology is now an accomplished fact throughout much of the world.

It is not coincidental that the early history of this evolution in the United States corresponds with passage of the National Cooperative Geologic Mapping Act, first authorized by Congress in 1992. The act established the National Cooperative Geologic Mapping Program (NCGMP), administered by the U.S. Geological Survey (USGS) and implemented through the USGS, the state geological surveys, and at more than 100 colleges and universities. NCGMP has several unique features but two in particular have pushed the use of GIS and IT for geologic mapping. First, those preparing new geologic maps funded by the program are encouraged to submit them to the USGS in digital format. Second, a state's final map products for an existing grant must be accepted by the USGS before that state is eligible to submit a new proposal the following year. Without GIS capabilities, the latter requirement especially is difficult to meet. As a consequence, and because much of the nation's nonacademic public-sector geologic mapping is centered in the USGS and state geological surveys, GIS and IT are now firmly established in the geologic mapping agencies of the United States.

Customized maps

The adoption of GIS and IT to create geologic maps is barely keeping pace with demands from the private sector for all kinds of geologic data in digital format. Both state and federal geologic mapping agencies face a customer base that expects to instantly receive a geologic map tailored to a specific need -- that is, a unique geologic map generated for a single client on demand. This reality has necessitated a profound shift in how agencies and field-oriented geoscientists view geologic maps and their creation. Traditionally, geologists were given great license to produce a geologic map. In the end, everything came together in a standardized paper-based geologic map that was reproduced in hundreds or thousands of copies. The customer was offered only one product. In essence, the traditional process of generating a geologic map used the individual geologist's preferences to generate a final standardized product. Public expectations today have turned that model upside down. The ability to produce a customized geologic map requires GIS and IT, and those technologies require a rigorously standardized store of georeferenced and logically related geologic data.

Given the rapidly growing demand for customized geologic maps, traditional geologic mapping skills are no longer sufficient. Individual mappers and agencies involved in producing these maps must now sort out the many nomenclature differences and disparate classification schemes that abound in geology so that GIS and IT can be used most effectively. Compromise and consensus are required to build logical data relationships in GIS and IT database systems. These requirements in turn are leading to a re-examination of the fundamental process of how field mapping is conducted and observations recorded and used.

Data standards

On the national level, the desire to create a new geologic map of the United States has elevated the long-recognized need to better reconcile geologic mapping across state boundaries and has focused many geologic mapping discussions on national standards proposed by policy groups sponsored by the USGS: Federal Geographic Data Committee (FGDC), North America Geologic Map Data Model Steering Committee, Content Standard for Digital Geospatial Metadata (CSDGM), Geologic Map Data Model, and others.

While these debates continue, a growing number of state geological surveys are adopting the draft standards as a common framework that allows open access to widely distributed georeferenced digital geologic data and its incorporation into geologic maps. NCGMP has provided a cooperative framework within which many problems are being worked out. One of the most effective of these forums is the annual Digital Mapping Techniques Workshop, convened by the Association of American State Geologists (AASG) and the USGS.

New products and applications

Laptop and hand-held personal computer programs with improved levels of utility are emerging from universities and public mapping agencies (Brimhall and Vanegas, 2001; Pavlis and Little, 2001; Black and Walker, 2001). These products are undergoing field trials and are moving geologic field-mapping data capture to the outcrop.

The use of GIS and IT throughout the geologic map-creation process is being closely paced by an expanding awareness that these technologies provide new opportunities for quantitative analysis of geologic map data. Now the association of GIS with relational database technology is being integrated with weight-of-evidence algorithms, logistic regression, and neural network modeling software to trace geologic bedrock units in areas of extensive cover; identify appropriate sites for special installations and development projects; guide zoning decisions; and support mineral exploration. Spatial Data Modeler, public-domain software used to implement GIS-based geologic data modeling, has been developed through a consortium guided by Graeme Bonham-Carter (Geological Survey of Canada) and Gary Raines (USGS) and is available online.

Geologists have long known that a comprehensive geologic map has many applications in the hands of a knowledgeable person. GIS and IT make it clear that a geologic map is no longer a static document. Any geologic map is now recognized as only one view of the geologic database from which it is derived. Many other derivative maps, created for specific purposes, can now be produced on an ad hoc custom basis. It is not unusual for the "standard" product of a modern geologic mapping project to include a bedrock map, a surficial geologic map, an engineering geology map, a geologic hazards map, as well as a classical comprehensive geologic map showing the relationship between bedrock and surficial units "as they face the sky." With proper planning, unique geologic maps or "views" can indeed be produced for individual customers.

These are exciting days for those who believe that the observation, collection, organization, and analysis of geologic field data provide the fundamental basis for subsequent geologic studies. Geologic map generation is in a period of renewal, with many innovative data capture and analysis methods coming into common use. The NCGMP, through its FEDMAP, STATEMAP, and EDMAP components, will likely remain a focal point for the continued evolution of geologic mapping in the United States. Certainly the cooperative programs developed among participating universities, state geological surveys, and the USGS have catalyzed significant progress to date. For readers not familiar with this program, a good source of information is the State Geologist of any state geological survey.


"Development and use of a laptop-based geological mapping system: Experience at the University of Kansas," by R. Black and J.D. Walker. In Digital Mapping Techniques '01 - Workshop Proceedings: U.S. Geological Survey, edited by D.R. Soller. Open File Report 01-223, p.127-131.

"Removing science workflow barriers to adoption of digital geologic mapping by using the GeoMapper Universal Program and Visual User Interface," by G.H. Brimhall and A. Vanegas. In ((Digital Mapping Techniques '01 - Workshop Proceedings: U.S. Geological Survey)), edited by D.R. Soller. Open File Report 01-223, p. 103-114.

Arc-SDM Arcview extension for spatial data modeling using weights of evidence, logistic regression, fuzzy logic, and neural network analysis, developed by D.L. Kemp, G.F. Bonham-Carter, and C.G. Looney, 2001.

"Using handheld personal computers as field data collection tools: Some lessons learned in the school of hard knocks in the Wingate Wash Project and related projects using FieldLog/Fieldworker software exported to ArcInfo," by T.L. Pavlis and Jason Little. In ((Digital Mapping Techniques '01 - Workshop Proceedings: U.S. Geological Survey)), edited by D.R. Soller. Open File Report 01-223, p.115-121.

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Wiltse is State Geologist of Alaska and director of the Alaska Division of Geological & Geophysical Surveys. E-mail.

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