GIS/GPS Integration: GPS Leads to GIS Western Style
While it is primarily rural and conforms closely to Hollywood's version of "the West" right down to the boots and cowboy hats, Mesa County, Colorado is anything but backward when it comes to GIS.
By Lisken Lewis Brady

GIS action on the Western Slope of the Colorado Rockies is easily overlooked, overshadowed by the intense activity along the Front Range, in metro Denver and environs. But the other side of the Continental Divide is busy with its own brand of GIS action.
      The vast Grand Valley is a fertile farming and ranching region, punctuated by small towns and criss-crossed by winding, one-lane roads. Mesa County covers 3,300 square miles of this rapidly growing region which lies flush against the Utah border. The county was just designated a metropolitan area in 1995, with an estimated population of 106,000. Grand Junction (pop. 31,758 in July 1994) is the hub of Mesa County. The Colorado River rushes right through this urban growth center.
      While it is primarily rural and conforms closely to Hollywood's version of "the West" right down to the boots and cowboy hats, Mesa County is anything but backward when it comes to GIS. The National Geodetic Survey (NGS) placed five HARN (High Accuracy Reference Network) points in Mesa County during the 1980s. Viewing these as an opportunity, the county proceeded to build the Mesa County Geodetic Control Network, the largest geodetic control network in the state. The Network is based on these five HARN points, which serve as the backbone for what has been named the "Supernet." The Supernet contains a total of 25 control points at this 1:1,000,000 level of accuracy. In 1993, Mesa County purchased three high-precision-type GPS receivers. That's when things really took off.
      "After building the Supernet, we went back in and tied a three-mile grid to it by GPS," explains Frank Kochevar, chief geodesist for the Mesa County Department of Public Works, in the survey section of the engineering division. Kochevar was hired by the county five years ago specifically to build this vast control network. "The surveyors realized that this is what it would take to get the GIS going," he explains. The Mesa County Geodetic Control Network now includes 168 main points throughout the Grand Valley. Additional points offer lesser accuracy but bring the total number of control points up to more than 400, including PLSS section and quarter-section points.
      "The advantage of this system is that there is no need for line of sight," says Kochevar. "This is very important because of the terrain." The northeast quadrant of the county boasts some particularly challenging formations, with peaks rising to above 10,000 feet. "But accuracy is the main advantage," continues Kochevar. "It's humanly impossible to obtain this level of accuracy with conventional surveying methods. The third advantage is ease of operation. Portability is very important." While some GPS units available today are no bigger than a hand calculator, those in use in Mesa County are about the size of a large dictionary. "We take them out and log data for 45 minutes to five hours, depending on the accuracy desired," says Kochevar. "We need four hours of occupation time on each point to obtain 1:1,000,000 accuracy."
      The county's focus on establishing a solid control network is now really starting to pay off. In early 1996, Mesa County asked Serion International (formerly SMARTSCAN Inc., and still located in Boulder, Colo.) to create a control network coverage for the county GIS, as well as county-wide parcel and street centerline coverages. The control network coverage was built during February and March 1996, using the Mesa County Geodetic Control Network GPS control points supplied by the county and supplemented by PLSS section corners. Once this preliminary control network was completed, Serion began the creation of other land base coverages. Approximately 53,000 parcels are being captured from a variety of existing digital and hardcopy sources. This phase of the project also involves the attribution of these parcels with the appropriate parcel numbers. The parcel number, mineral rights text and platted block numbers are also placed as annotation. Historic lot lines are captured from the mylars as a separate linear coverage with the lot number as annotation. Centerlines are captured as a linear coverage for road and railroad rights of way and are attributed with data from three different source files.
      As is so often the case these days, in addition to hardcopy-to-digital conversion, digital data conversion is necessary to complete the coverages required by the Mesa County GIS. Fifteen AutoCAD files existed, some consisting of more than one township. All of this data was in the County's coordinate system, and most consisted of line work and a block with the parcel number attribute attached and placed within an area of the parcel. Serion is cleaning up some of this line work during this process to make the data topologically correct for ARC/INFO. Then all the files are translated to be merged with the newly created coverages. The newly converted data is then edge-matched to existing data and delivered to the county in both ARC/INFO Export and AutoCAD DWG formats. Check plots are created for each of the 150 mylar maps, and the images are delivered in a binary RLC ARC/INFO format that is compatible with Mesa County's GIS.
      "Because the pilot was both fast and thorough, it showed us exactly what the product would ultimately look like," says Rick Corsi, GIS coordinator for Mesa County. "We changed a spec or two and some aspects of the line work based on the pilot. Doing the pilot really helped the conversion go smoothly."
      When the completed coverages arrives at Mesa County, it is tiled into logical divisions and the maintenance process of keeping the coverage up-to-date begins immediately. The coverage is used in a variety of ways by several county departments, as well as by a number of outside agencies and private businesses.
      Parcel identification is the main link to all of the county's databases for GIS purposes. This means that the development of the parcel layer provides direct geographical access to the assessment system, the building permit system, voter information, property information and other important data: • The county assessor will soon be able to use the parcel coverage to identify, locate and compare properties.
• Planners will be able to evaluate county growth trends, future development directions and it will come in handy during the upcoming county land use review process.
• Engineering is planning to use the GIS to analyze traffic patterns, determine road development priorities, evaluate and document road conditions, and to maintain an equipment inventory.
• The building department will be able to locate properties and use parcel numbers to access other useful databases.
      The updated centerline coverage will be used to bring the county road map up to date, to develop an E911 coverage, and to provide the U.S. Census Bureau with an updated road coverage for use during the 2000 census.
      "GPS has enabled us to build a very accurate coverage to tie our parcel coverage to in a very short time," says Corsi. "Without the GPS control, we would not have been able to tie the parcel map down with the accuracy that we needed. GPS will continue to play a large role in our GIS as we continue to collect GPS control and refine the accuracy of our coverages."

About the Author:
Lisken Lewis Brady is a technical project manager for Serion International & SMARTSCAN, Inc. She has worked closely with Mesa County to ensure the success of this project. She may be reached at 303-443-7226 (phone), 303-443-2997 (fax) or e-mail: [email protected]

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