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Accuracy of Data - GPS controls our data

The geodetic control that Mesa County uses to define the geographic locations of our data started well before a GIS was ever envisioned. During the 1980s the National Geodetic Survey (NGS) placed five HARN (High Accuracy Reference Network) points in Mesa County. The County proceeded to establish the A Mesa County Geodetic Control Network", the largest geodetic control network in the state, based on these five HARN points, using Global Positioning System (GPS) survey technology. The positioning of these points has assisted the County in creating a standardized monumentation grid for public and private surveys as well as setting the stage of control for the development of an accurate countywide digital base map. The County's Engineering Department has continued to build what has been called the SuperNet of over 1000 main control points throughout the Grand Valley. Additional points surveyed using GPS for GIS purposes offer less accuracy, but bring the number of control points to more than 2000. They include PLSS sections and quarter-section points.

Public Works has used GPS for GIS related projects that include: locating road centerlines for over 3000 miles of roadway, geocoding and data linking of County maintained bridges and culverts, and coding utility permit information. Mesa County GIS and other County departments have assisted Mesa State College, CSU Agricultural Extension Office, Center for Disease Control, the Health Department, law enforcement and others with GIS/GPS related projects.

In 1996 Mesa County installed a GPS Community Base Station with a public dial-in BBS which was the only one in this part of the state. This allowed county surveyors and anyone within 300 miles to do post processing differential correction of GPS data without having to setup an additional receiver on an established point. Today 3 CORS base station are running in the County including 1 NGS COOP station to provide high precision/real time system making it possible for surveyors to receive corrected data as they survey in the field without setting up additional receiver/transmitters on high accuracy points. This is the only publicly available system of its type in the western United States. The differential correction data files are now available via the Internet on the County's ftp server.

What does this mean for GIS? It allows the County and others to collect data faster and more accurately, increasing the information we have available and reducing the cost of data collection. GPS has proven to be a fast and low cost method of collecting data and providing the real world control for our GIS. The future of GPS in GIS is becoming more and more obtainable as technology advances and equipment cost declines.

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