Digital Mapping Techniques '97
U.S. Geological Survey Open-File Report 97-269

Digital Mapping Projects at the Florida Geological Survey

By Jonathan D. Arthur

Florida Geological Survey

903 W. Tennessee St.

Tallahassee, Fl, 32304

Telephone: (904) 488-9380

Fax: (904) 488-8086


Since 1989, the Florida Geological Survey (FGS) has been engaged in digital mapping of local and regional surface and subsurface geology. The process has involved data transfer from paper maps to the computer-aided design (CAD) program, AutoCAD. In late 1996, the FGS acquired the requisite hardware, software and technical support to begin geographic information system (GIS) product development. Three digital mapping projects are in progress: 1) the statewide geological map of Florida; 2) subsurface mapping of lithostratigraphic and hydrostratigraphic units in Southwest Florida; and 3) a detailed geologic map of the Sarasota 1:100,000 quadrangle.

Statewide Geological Map

Revision of the 1964 version of Florida's geologic map began in the late 1980's in response to the need for a peer-reviewed map that reflects current field data and lithostratigraphic nomenclature of surficial geology in Florida. In 1992, a grant from the Florida Department of Community Affairs (DCA) was obtained to support the project. DCA interest pertained to health concerns about radon and its relation to geological units in Florida. The grant, in the amount of $99,000, provided support for mapping Florida's 67 counties over an 18 month period. Six FGS staff geologists were involved in the mapping project. At the end of the grant period, continued financial support for this project came from FGS internal funds.

In Florida, surface sediments are comprised primarily of Holocene quartz sands with limited rock outcrops or exposures. Standard geologic mapping of outcrops was thus not a viable option for this project. As a result, mapping standards were developed to enhance geological detail: the Geologic Map of Florida is a sub-crop map that represents the uppermost geological unit observed within 20 feet of land surface. In areas where cover sediments are less than 20 feet thick, the underlying unit is mapped. If cover sediments exceed 20 feet in thickness, they are mapped as "Quaternary undifferentiated."

Geologic unit "contact" lines were hand drawn on base map 1:24,000 quadrangles. Contour lines on these maps were used as a guide for estimating sub-crop formation contacts according to the 20 foot mapping standard. The contact lines were then transferred by hand to Florida Department of Transportation maps (1:125,000) and then digitized using AutoCad (ver.10 through 12/DOS). Control points for the maps included the results from field mapping and lithologic descriptions of several hundred cores and cuttings sets. These samples were selected from the FGS core repository, which contains more than 17,500 sets of borehole cores and cuttings.

Base maps for this project were US Geological Survey 1:24,000 quadrangles. These maps were digitized using early versions of AutoCad and a composite basemap of the state of Florida was generated. Two FGS cartographers were assigned to this task during the DCA grant period. Hardware available during this phase of the project included two 486 IBM-compatible computers with at least 8Mb RAM, two digitizing tables (48" x 60") and a pen plotter. A Novell network was set up in 1993 in response to the increased need to share hardware devices, and to store, manage and backup large data files. In 1995, FGS network facilities were upgraded to Windows NT with full Internet access and e-mail capabilities.

Base maps and geologic map data were compiled by county and published in the FGS Open File Map Series (OFMS). This publication format was created to provide an interim source of information to the geological community until the statewide map becomes available in either digital or paper format. The OFMS maps were plotted at a scale of 1:125,000. Copies of the county geologic maps are available on the Internet in *.dxf format from

The statewide geologic map is an edge-matched compilation of the county maps. In 1997, this composite map has been exported as a .dxf file into the GIS software package, Arc/Info (ver.7.1). Map topology is presently being developed and will be followed by attribute definition. The map will be peer-reviewed in the second half of 1997 and a final paper version will be published in color at a scale of 1:750,000. The map, supporting text and metadata will be included in the Florida Department of Environmental Protection GIS Map Library. The final copy will become available on the FGS Internet web site as well. The format is yet to be determined.

Southwest Florida Subsurface Mapping Project

This four-year project is a cooperative agreement between the FGS and the Southwest Florida Water Management District (SWFWMD). Research began in 1995 with the development of an extensive database containing more than 4,800 wells in the southwest Florida region. Funding for this part of the project totaled $15,000. The database contains all available information on the wells pertaining to location, construction, use, and types of geophysical and lithologic data. Once complete, this database was used to screen wells appropriate as control points for the subsurface mapping project, which will continue until 1999. The mapping phase is presently funded at $80,000 per year for three years. Each year, one third of the approximately 10,000 square mile study area will be mapped. Products to be generated include structure contour and isopach maps for Eocene and younger lithostratigraphic units and all regionally extensive aquifer systems, including permeable zones and confining units. The units for which the maps will be constructed are listed below:

Hydrostratigraphic units

Lithostratigraphic units

Surficial aquifer system


Intermediate confining unit and aquifer system

Hawthorn Group

Floridan aquifer system

  Peace River Formation

Sub-Floridan confining unit

  Arcadia Formation


    Tampa Member


    Nocatee Member


Suwannee Limestone


Ocala Limestone


Avon Park Formation

Database development utilized Paradox for Windows (ver.5). Basic well information had been entered into a spreadsheet prior to the beginning of this project. Data entry forms were designed to complement data existing in spreadsheet files. Information from drillers logs, geophysical log "header sheets," and index cards for each well were entered through use of the forms. Many of the wells were drilled prior to 1970 and a majority of the location information available was limited to Public Land Survey Coordinates (PLS). As such, the most accurate location for most wells was limited to the extent of a PLS section (i.e., somewhere within one square mile). Lack of sufficient funds and time precluded global positioning system (GPS) field confirmation of the more than 4,800 well locations.

Since any GIS-compatible database requires specific attribute coordinates (i.e., latitude-longitude or UTM) for a well location, each well was assigned a location accuracy value (meters radius), which becomes important when estimating well-head elevations for older wells. Elevation uncertainties translate to uncertainties in the mapped subsurface horizons. Locations accuracy values were determined by hand plotting all wells on 1:24,000 quadrangle maps using the most accurate, available location information, then calculating a maximum radius of uncertainty. For example, if the best available location for a well identifies only township, range, and section (TRS), the well is plotted in the center of the section and has a location accuracy value (radius) of 1138m. This value reflects the distance from the center of the section to any corner of the section. In order to determine Cartesian coordinates of wells plotted by TRS, each map was "locked down" using AutoCAD and through a script program, latitude-longitude and UTM coordinates were calculated and exported into ASCII text files. These files were then imported into the Paradox database. Typographical errors in location coordinates were almost completely avoided by utilizing this technique.

Once complete, the database was queried to provide a list of potential control point wells for the subsurface mapping project. Selection of control wells was based on sample location, quality (including sampling interval for cuttings) and total depth. Control point coverage for each horizon mapped is one well per 10 square miles. Although this is possible for the shallower units, deeper horizons, such as the sub-Floridan confining unit, will have less coverage due to a limited number of wells that penetrate the unit. Where possible, geophysical logs, primarily gamma-ray logs, will be evaluated for formation-contact estimates based on correlation of the logs to local stratigraphy.

Thirty cross sections generated from a separate FGS-SWFWMD cooperative study will be valuable correlation reference tools especially with regard to gamma-ray log response. Cores and cuttings from the SWFWMD Regional Observation and Monitoring Project (ROMP) wells were used in the cross sections. SWFWMD funding for the cross-section project, which began in 1992, has been $15,000 per year and is projected to continue into 1999. The cross sections not only depict regional lithostratigraphy and hydrostratigraphy, but also gamma-ray logs, topographic profiles and accessory minerals. An early effort to produce subsurface maps utilized formation contact boundaries from these cross sections. The data was imported into Arc/Info and the Arc/Info Triangular Irregular Network (TIN) module was used to contour the data.

The database to be used for the Southwest Florida Subsurface Mapping Project will at least double the control point coverage used in the above-referenced TIN mapping effort. Contouring and map generation will apply the ArcView Spatial Analyst. Final stages of map generation will include consideration of boundary conditions, structural features and karst features. The final peer-reviewed maps will be published, added to the DEP GIS map library and will be available through the Internet.

Sarasota Quadrangle Geologic Map

This mapping project began in 1996 and is funded equally by the FGS and the STATEMAP component of the USGS National Cooperative Geologic Mapping Program. Total project funding is $140,000. Detailed mapping of the 1:100,000 Sarasota County quadrangle is being conducted on a series of 1:24,000 base maps. In contrast to the statewide mapping project, this map will provide much more detail due to more extensive field mapping, data collection, review of local government files and drilling of six exploratory shallow cores (<50' depth) using a Mobile auger drilling rig. County or regional agencies such as the SWFWMD, and Sarasota and Manatee County Health Departments, etc. have water-well and plugging-permit files that contain geological data from local drillers and consultants. This information, coupled with visits to mining and excavating operations will add significant detail to the map.

One challenge that exists in the development of this map is delineation of the Pliocene-Pleistocene units. Historically these units have been mapped based on biostratigraphy rather than lithostratigraphy. As such, many of these older units will be incorporated into more generalized sub-crop units. Mapping criteria is the same as that of the statewide geological map -- the uppermost geologic unit within 20' of land surface. The final product will be digitized in Autocad (ver.12), on a 1:100,000 Sarasota quadrangle basemap. Included on the map will be a description of the regional geology and up to four cross sections.

Summary and future directions

Digital mapping at the Florida Geological Survey has come far since the first digitized products were completed as early as 1989. The first hardware configuration included an IBM-compatible 386 computer with a math co-processor, 2Mb RAM, a small digitizing pad and plotter. Present facilities include Pentium computers, a Sun Microsystems Ultra2 workstation, two x-terminals and an HP Designjet 750C plotter. Software used for digital mapping has evolved from AutoCAD version 10 to version 12, and mapping has just begun using Arc/Info and ArcView. Today, core drilling sites and surface samples are located using GPS, rather than estimating locations on 1:24,000 quadrangle sheets.

Future digital mapping projects at the FGS include a revision of the physiographic map of Florida and continued work on STATEMAP and water management district projects. Digital maps produced by the FGS are useful toward ecosystem management, environmental protection, solid-earth resource assessment and permitting, rules enforcement, conceptual frameworks for ground-water flow models, and baseline geologic and hydrogeologic research.

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Maintained by Dave Soller
Last updated 10.07.97