Investment in digital orthographic coverage leads to wider cost-saving through collaboration.

By Bill McGarigle

Spatial data is not only a catalyst for innovative applications, it adds a visual dimension to knowledge and decision-making that can empower government, business and citizens alike. Now with the synchronicity of Web-based software, interoperability standards, distributed databases and high-resolution aerial and satellite photography, a wealth of imagery and graphic information can be added to e-government services.

Several local governments in Pima County, Ariz., demonstrated this recently. What began as a project by Tucson, Ariz., to replace 20-year-old floodplain contour maps with digital orthophotography, quickly grew into a regional project that extends the benefits of spatial data to other jurisdictions and to private firms and citizens.

Faced with the need to develop new floodplain contour maps, determine the area of impervious ground and carry out habitat repair, Tucson decided to use high-resolution orthographic photography and related terrain data rather than update 20-year-old maps. The initial plan was to acquire coverage for the project areas alone, in one-foot resolution black and white, and one-meter resolution color, along with the associated terrain data. In discussing the proposed acquisition at meetings of the Pima Association of Governments (PAG), other local governments became interested and proposed expanding coverage to include their jurisdictions. Shared procurement offered the most cost-saving approach to acquiring the data.

As more jurisdictions signed on, PAG members determined that expanding coverage to include the eastern part of the county would benefit many agencies, as well as the larger community. In 1998, PAG was directed to handle the RFP and contract for one-foot resolution grayscale, one-meter resolution multispectral digital imagery and associated

terrain data. The coverage area -- 578 square miles of Pima County -- included Tucson as well as Marana, Oro Valley and Sahaurita. The overall cost of the data and processing was $2.3 million, most of which was provided by funding from the Federal Highway Administration. The remainder was made up of matching funds from the county, the five cities and towns in the region and the Tucson Airport Authority.

Cost-Saving Applications

Ron Platt, program manager for Tucsons maintenance division, said that once engineers and surveyors had the imagery, they began to see possibilities for numerous applications. By November 1999, agencies in the various jurisdictions were incorporating the new data in GIS solutions, using the imagery as a base to map overlays in hydraulic studies, make tentative plat maps and preliminary roadway designs.

"County engineers were developing floodplain contours and building three-dimensional terrain models, without leaving the office," Platt said. "These studies are used primarily to identify and measure cross-slopes of environmentally sensitive peaks and hillsides excluded from development."

Platt said jurisdictions were experimenting with the data and developing new techniques for local and joint use. He pointed out that the data was first used by the Tucson Department of Transportation and County Flood Control to do a hydrologic study along a 12-mile section of the Rillito River. "Because the consultant didnt need to purchase terrain-modeling data, that project alone saved the county between $50,000 and $100,000."

Tucson is currently using the data to inventory streetlights, checking the number and location of each light against construction plans. PAG project manager, Manny Rosas, said the city and county are using the data to develop a geodetic network throughout the region. Iformation on this is available on-line. Rosas explained, "The network is tied to the National Geodetic Survey Reference System, which is essential for intelligent transportation systems and GPS-based vehicle navigation."

At the county level, the accuracy of the ortho imagery is enabling engineers to measure the linear distance of road segments to be paved, and predetermine the amount of surface material required.

According to Platt, the process saves time and cuts down considerably on engineering