Lewis and Clark County, Mont., Updates GIS System

‘With more than 8,500 existing sites that need to be mapped, we had to be able to collect locations accurately and more efficiently than we could by measuring distances to property corners and triangulating well, septic and field locations’

Lewis and Clark County, Mont., http://www.co.lewis-clark.mt.us/ has found an innovative way to tackle a major civic mapping project. Officials there are using the GPS-based MobileMapper from Thales http://www.thalesnavigation.com/en/index_flash.asp to help build database of the county’s septic systems, treatment fields and domestic water supply wells.

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The environmental services division of Lewis and Clark’s city-county health department is saving time and money by using the MobileMapper units to take over from the traditional labor-intensive triangulation methods used in the past. "Our goal is to be able to provide residents and developers with the precise location of wells and waste water treatment systems for all property parcels in the county," said Frank Preskar, environmental health specialist. "With more than 8,500 existing sites that need to be mapped, we had to be able to collect locations accurately and more efficiently than we could by measuring distances to property corners and triangulating well, septic and field locations."

This past June, at the suggestion of the county GIS manager, who had used and evaluated MobileMapper in other applications, the department investigated the suitability of the Thales GPS-based data collector for its mapping needs. MobileMapper’s "consumer-like" ease of use simplifies the task of recording location points and entering descriptive information associated with the points. With 2-3 meter real-time accuracy and sub-meter post-processed accuracy, direct download capability to GIS programs, and a cost of less than $2,200 apiece, with post-processing MobileMapper proved to be the right choice. The initial results were so impressive that the department purchased further units in the fall.

The county’s environmental services division is responsible for a host of programs that work to protect public health and the environment. The on-site wastewater program and subdivision review protect the public from surfacing sewage and act to maintain the quality of the county’s groundwater.

"We’re just starting to collect the data and download it into our ArcMap program," said Preskar. "The data is also provided to the county’s master GIS databases. To date, we’ve completed about 50 sites. The MobileMapper cuts time to job completion in half. Previously, everything was done in hard copy using rough sketches. We measured with tapes to property corners and triangulated the positions."

That can be enormously time-consuming, according to Preskar, particularly on 30- and 40-acre parcels. Previously all hard copies were filed according to who owned the property. As property changed hands, it became increasingly difficult to find the information.

"We’ve done away with all that hand-sketching," Preskar said. "Now we go to the property and simply collect the points we need and key in the descriptive data from a feature library loaded on the MobileMapper. The library is set up with five fields: monitoring wells, test holes, septic tanks, drain field and wells. Back in the office the MobileMapper software enables us to upload the information as a SHP file to our computer and import it into our ArcMap desktop application program. ArcMap enables us to compose maps showing all the points and descriptions we’ve collected. Pages can then be composed for printing and publishing for each parcel."