Erasing Borders

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

by / September 26, 2000
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 consulting fees. "It enables assessors, planners, engineers, surveyors and many others to find what they are looking for in ortho images without leaving their desks. I would guess 1,000 plus people a day save a trip this way. All that is a direct benefit to the public."

Other applications include developing topographic maps with two-foot and four-foot contour lines, replacing inaccurate TIGER files with street centerline maps for more accurate census data. For reassessment purposes, the county assessor can overlay parcel boundaries on the orthophotography and check for exterior improvements -- for example, swimming pools, tennis courts, small cottages -- that for some reason were not picked up by the assessors office.

Building Public Access

Providing public access to the data over the Internet was the next step. "The data was paid for by taxpayer money," said Jack Avis, Pima County GIS Manager. "We wanted to turn it around and make it available at a nominal reproduction cost to anyone who might have a need for the imagery or the derived terrain data." With a $20,000 grant for software
and hardware from ESRI and a file server donated by IBM, PAG was directed to coordinate the development of a portal that would allow ready access to the data and its features. The result is the Regional Data Distribution Center (RDC), which opened in June. The portal is designed around ESRIs ArcIMS, Autodesks MapGuide and an IBM file server, and can be accessed at .

Visitors can view topographic maps and orthophoto imagery in black and white or color, select a feature or geographic area of interest and turn data layers on and off -- for example, overlay boundaries of parcels, parks, street networks or jurisdictions. They can select 3D views, click on parcels and other locations for related information of
public record, access demographic data, metadata and the public land-information system. They can perform basic GIS analysis, study a tutorial, or enroll in an online workshop on how to view and use the data.

"We didnt realize at the time," Platt said, "that the Internet was going to play such an important part in delivery of this information. The site has allowed realtors, appraisers, assessors, surveyors, engineers and the general public to just bop in and look at the orthophotos at their convenience and come up with their own

Rosas pointed out that in addition to the general public, the RDC Web site is also attracting developers, realtors and others in the private sector. "Realtors can show the part of town that prospective clients are interested in. They can identify parcels with the relative criteria -- hillside properties, schools, shopping areas, parks -- then overlay GIS layers on top of the orthophotography. They can pull up 3D images to get an idea of the topography of an area, then check out its demographics. With a resolution of one foot, viewers can see hiking and riding trails and zoom in to identify objects as small as three feet square. Clients can begin making decisions right from the desktop."

"Engineering consulting firms are particularly interested in the visual information the accuracy provides," Rosas added. "They are using the data to assist in drainage studies associated with road improvements. It allows them to view watersheds, make hydrology calculations and calculate flow rates of specific drainage basins. Information like this is helpful in a variety of engineering applications, for example, determining the substructure of a bridge, how deep the support pylons must be."

The site also has information and features that can be accessed only by jurisdictional members who are responsible for maintaining and updating their respective data layers and posting changes on the Web site. The Pima County Department of Transportation, Technical Services Division,
maintains the parcel base layer. Assessment maps and the parcel layer itself are under the jurisdiction of the County Assessors Office. The Technical Services Division also maintains a hundred-plus GIS layers. Although viewers are not seeing realtime data, updates are delayed by no more than 24 hours.

Plans for Expanding

"The benefits of the data have been tremendous," Avis said. "PAG is in the process of writing specifications for additional orthophotography. This year we will be soliciting another RFP and going after more orthophotography. There are other areas in the county that need coverage, and we hope to continue providing that over the next few years, maintaining a working data set. In the future, there will be re-flights of areas that have significant changes, acquiring new photos and data as they are needed."