The California Department of Conservation's Division of Mines and Geology (DMG) uses three Geographic Information Systems (GIS) platforms for a variety of applications. Arc/Info is used for digitizing basic data such as geologic, landslide, and fault maps. MAPINFO is used for planimetric map applications and INTERGRAPH is used for generation of seismic hazards zones maps that integrate surficial and subsurface data . DMG map digitization activities have evolved from a close cooperation with the U.S. Geological Survey (USGS). DMG uses Sun workstations running Arc/Info software. The ALACARTE interface developed by the USGS is used to simplify digitization. DMG employs students to do geologic map digitization under the supervision of staff geologists. A typical 7.5-minute quadrangle takes about 100(+-)40 hours of student operator time and about 40 hours of geologist time for supervision and review. The labor cost for a typical 7.5-minute quadrangle is about $2300(+-)600. Digitizing a 1:100,000 quadrangle is accomplished by using the largest available source data, preferably 1:24,000 at a total cost of about $143,000. DMG digitizes geologic maps at a scale of 1:24,000 and publishes regional maps at 1:100,000 scale. The reasons for this are: 1) hazards maps prepared by DMG for regulatory and planning purposes are 1:24,000 scale and require basic geologic map data at the same scale; 2) 1:24,000 is the most commonly requested map scale by geologic map users in California; 3) most of the densely populated urban areas in California are geologically complex that require 1:24,000 scale to portray the necessary detail. In the absence of geologic data at appropriately large scale, small scale maps are enlarged for application for which they were never intended. DMG has not released digital geologic maps for general distribution pending development of polices and procedures for release of digital products. Although most of our users still need paper geologic maps, DMG recognizes the future is in digital geologic maps.
The California Department of Conservation's Division of Mines and Geology (DMG) is employing three Geographic Information Systems (GIS) to produce digital maps for a variety of applications. Digital maps include geologic, landslide, fault, geologic hazards, mineral resource evaluation and probabilistic ground response maps. Geologic, fault, and landslide maps provide basic data used in the preparation of regulatory maps (Earthquake Fault Zone Maps; Seismic Hazards Zone Maps) and for probabilistic analysis to produce site response maps that serve as a
basis for amendments to building codes and establishing earthquake insurance rates. Some of these maps can be accessed on the Department of Conservation's website (http://www.consrv.ca.gov/dmg/) and more will be added in the near future. The GIS platforms employed by DMG are:
ARC/INFO used for digitization of geologic maps, fault maps, and landslide maps;
MAPINFO used for planimetric map applications such as map indexes, some probabilistic site response maps, mine location maps, mineral commodity maps, and fault maps;
INTERGRAPH used for preparation of online Seismic Hazards Zones Maps that integrate and analyze geologic map data converted from Arc/Info, subsurface data, and digital elevation models to show areas prone to ground failure during earthquakes.
This paper discusses the digital mapping techniques used by DMG's Regional Geologic Mapping Project to prepare digital geologic maps using Arc/Info. The objective of digital geologic mapping by DMG is to produce a digital database of geologic mapping in California that will be readily available to earth scientists, engineers, planners, decision-makers, and the public. The Regional Geologic Mapping group is in the process of converting from the production of analog geologic maps to digital maps. Geologic maps presently sold by DMG are analog produced by conventional techniques. Although digital geologic maps have been prepared and have been used internally and released informally, the policies and procedures for distribution of digital geologic maps have not been established.
The first use of digital technology in geologic mapping by DMG was in 1984. It was used to contract for the scanning of a 1:250,000 scale geologic map to prepare printing plates instead of conventional scribing techniques. This attempt failed because the contractor did not have any knowledge of geologic maps and DMG staff did not know how to prepare the map for scanning. After a year delay, the map was scribed and published using traditional techniques.
DMG geologic map digitization activities have evolved as a result of close cooperation with the U.S. Geological Survey (USGS). In 1990, DMG began a cooperative geologic mapping project in southern California with the USGS, the Southern California Areal Mapping Project (SCAMP) of the USGS. A GIS laboratory supported by both agencies was established at the University of California campus at Riverside. In 1993 a workstation was set up in DMG offices in Sacramento. Since 1995, DMG geologists have been digitizing geologic maps in USGS offices in Menlo Park, California on a part time basis. DMG and the USGS are establishing a cooperative geologic mapping program in the San Francisco Bay area (BAYMAP) similar to the southern California project. DMG is now setting up additional workstations in Sacramento and in its San Francisco Regional office.
Preliminary digital versions of the Geologic Map of California (Jennings, 1977) and the Fault Activity Map of California (Jennings, 1994), both at 1:750,000 scale have been produced by the USGS in cooperation with CDMG. In 1991 Gary Raines of the USGS proposed digitizing the Geologic Map of California for use in the mineral resource analysis of the western United States. He was provided with stable base materials with the understanding that the digital map would be for internal USGS use and the ownership and distribution rights for the map would remain with DMG. The digitization was done by a private contractor. DMG is now revising and editing the map. DMG has been providing the files to users who have an immediate need for them provided they agree not to distribute the files. Michael Machette of USGS digitized Quaternary faults from a preliminary version of the Fault Activity Map of California for use in preparation of a Quaternary fault map of the United States. DMG staff updated the files after the final version of the Fault Activity Map of California and Adjacent areas was published in 1994. A digital database of Quaternary faults in California will be released soon.
DMG uses Sun workstations running UNIX-based Arc/Info software to digitize geologic maps. DMG uses the ALACARTE interface developed by the USGS (Fitzgibbon and Wentworth, 1991). ALACARTE, a program specific to digitizing geologic maps running on top of Arc/Info, enables an operator without an extensive knowledge of UNIX or Arc/Info to digitize geologic maps. ALACARTE provides line types and symbol sets commonly used for geologic maps and greatly simplifies the placement and orientation of geologic symbols.
Although some digitization is done by staff geologists, most of it is done by students under the direct supervision by staff geologists. We have had success employing students majoring in geology who have training in GIS. Geology students who have training in GIS (usually taught in geography classes) are hard to find but they are becoming more common. We have had success with students without GIS training but they require more supervision, thus raising the costs because of increased staff time on the project. DMG has initiated interagency agreements with both the California State University and the University of California systems to provide students to do digitization. This has proved to be cost effective for DMG as well as providing employment opportunities and on-the-job training for students.
The goal of DMG is to assemble a statewide database of geologic mapping at a scale of 1:24,000. Of the 2,832 7.5-minute quadrangles in California, an estimated 2,257 have not been mapped. Obviously, this long-term goal is a formidable challenge. A rationale for this approach is discussed in the Data Capture Standards section of the paper. Historically, the publication scale for regional geologic maps in California has been 1:250,000. The complexity of the geology in many areas and the availability of the base maps at 1:100,000 scale prompted the switch to a larger scale.
In the past, DMG compiled an analog version of a 1:100,000 scale geologic map prior to digitizing. This can take one to three years depending on how much original mapping is conducted and the geologic complexity of the map area. As our digitizing capability has improved, we are beginning to move away from this approach. A major task that still must be completed, however, is the preparation of a stratigraphic framework for each 1:100,000 quadrangle. The complex geology of California poses special problems for regional syntheses. A typical 1:100,000 scale quadrangle in California has 80 to 120 geologic units and some may have even more. The state has been divided into 11 provinces based on geology and physiography. Most 1:000,000 scale quadrangles cover more than one province, so parallel stratigraphic frameworks must be established. Some map units are common among adjacent provinces but many are not. In particular, stratigraphic columns on either side of major strike slip faults are different. For example, our compilation of the Monterey 100K quadrangle has two explanations, describing units on either side of the San Andreas fault. A stratigraphic framework for a 1:100,000 quadrangle is prepared, reviewed, and accepted before digitization of the 1:24,000 quadrangles that make up the regional map. The preparation of the framework is critical to producing a seamless 1:100,000 geologic map mosaicked from thirty-two 7.5' quadrangles.
The DMG procedure in digitizing a 1:24,000-scale geologic map is as follows:
The times above are approximate. Operator's time for a typical 7.5-minute quadrangle is about 100(+-)40 hours. Geologist's time for supervision and review is about 40 hours.
A Sun workstation ranges from about $12,000 to over $30,000 and the Arc/Info license costs about $17,000. Scanners cost about $ 30,000 to $40,000 and a 48 x 60 inch digitizing tablet costs about $9,500. A plotter suitable for plotting geologic maps ranges from about $7,000 to over $10,000. Supplies cost about $1,000 to $3,000 per year.
Compilation of an analog version of the 1:100,000 scale geologic map is about $100,000 per year. At one to three years, such a compilation is often not affordable despite its usefulness. If an analog version of the map is not prepared, a geologist still must prepare a stratigraphic framework (i.e., map explanation) that will require three months or about $25,000. Operators (students) cost an average of $10 per hour and staff geologists average about $32 per hour. Therefore, an average cost for this method is $1,000 for the operator and $1,280 for the geologist. For planning purposes the labor cost for digitizing a 7.5-minute quadrangle is $2,300(+-)$600. Using the estimate of $2,300, the cost of digitizing a 1:100,000 quadrangle (32 7.5-minute quadrangles) is $73,600(+-)$19,200. This does not include equipment cost, support staff, and overhead which will substantially increase the ultimate cost.
Summary of labor costs for digitizing a 7.5-minute
Operator (student; 100 hours @ $10/hour) $1,000
Geologist (40 hours @ $32/hour) $1,280
Costs of digitizing a 1:100,000 quadrangle:
Preparation of stratigraphic framework $25,000
Digitization of 32 7.5' quads
@ $2,280 each $72,960
Support staff $12,000
Overhead (30%) $32,988
DMG digitizes geologic maps at a scale of 1:24,000 and publishes regional maps at 1:100,000 scale. The reasons for this are: 1) hazards maps prepared by DMG for regulatory and planning purposes are 1:24,000 scale and require basic geologic map data at the same scale; 2) 1:24,000 is the most commonly requested map scale by geologic map users in California; 3) most of the densely populated urban areas in California are geologically so complex they require 1:24,000 scale to portray the necessary detail.
DMG has been criticized for high costs of digitizing geologic maps in its USGS National Cooperative Geologic Mapping Program STATEMAP proposals. Digitizing 32 1:24,000 scale maps and assembling them into a seamless 1:100,000 geologic map is a far more time consuming, expensive proposition than scanning a map at 1:100,000 scale. Many uses for geologic maps in California require 1:24,000 scale. Where such maps are unavailable, the smaller scale maps are used improperly. There are many instances of maps being enlarged to unreasonable extents because larger scale maps do not exist. This is not a new problem; small scale regional geologic maps have been enlarged and misused before, but digital maps can be abused far more easily than conventionally printed maps.
DMG has prepared digital geologic maps in fulfillment of contracts for STATEMAP and for the DMG Seismic Hazards Zoning Program. DMG has not released digital geologic maps for general distribution pending development of polices and procedures for release of these products. Although most of our users still need paper geologic maps, DMG recognizes the future is in digital geologic maps. DMG derives revenue from the sale of its publications; cost recovery is an important consideration. It is uncertain how or if costs of digitizing maps can be recovered. An evaluation of on-demand printing of maps versus large press runs of maps is underway.
Fitzgibbon, T. T. and Wentworth, C. M., 1991, ALACARTE User Interface-AML Code and Demonstration Maps: U.S. Geological Survey Open-file Report 91-587, 10 p.
Jennings, C. W., 1977, Geologic Map of California: California Division of Mines and Geology Geologic Data Map No. 2, scale 1:750,000.
Jennings, C.W., 1994, Fault Activity Map of California and Adjacent Areas: California Department of Conservation, Division of Mines and Geology Geologic Data Map No, 6, scale 1:750,000.