Zooming in

When Modesto, Calif., started developing a citywide geographic information system (GIS) seven years ago, many utility features “didn’t appear where they belonged on the basemap,” says Gary Wiseman, city surveyor. The GIS basemap had been developed years ago by the county Public Works Department, and was accurate to 10 feet in most places, while others were off by as much as 100 feet, according to Wiseman. For its time, the map was “pretty decent as far as accuracy, but not accurate enough to display the information being collected with GPS and other high-accuracy survey equipment,” he says.

The city had begun using high-accuracy global positioning system (GPS) survey equipment — a compact GPS unit, or rover — for the field and a permanent reference station on the administration building that helped workers locate city infrastructure within centimeters or better accuracy. But when they added a newly located manhole to the GIS, for example, it would show up on the basemap in the middle of a lot. The city then would have to move the feature to where it appeared correctly on the map, in the street. “It got to be such a hassle to fix things that, basically, we started over,” Wiseman says. “The GIS was the driving force to get money budgeted to improve the basemap.”

Starting over for Modesto meant hiring and training four computer aided design technicians in 2003 to perform computerized line work, while Wiseman established the framework on which the basemap was built. It took staff 15 months to finish — but with ongoing maintenance and updates for the growing city, it’s “a never-ending project,” Wiseman says.

Using the same GPS equipment that captured its infrastructure, the city created an accurate basemap, which GIS Coordinator Robert Beckler used to improve GIS data sets. “Now all the data fits together,” says Beckler, who spearheaded the city’s GIS initiative. “There’s no more data massaging, and it significantly reduces the time required to bring new data assets online.”

Today, Modesto is updating much of its location data. As a result, those depending on that information are more confident about its quality and, thus, their ability to respond to any situation — including emergencies. “An accurate, up-to-date GIS provides better information and data availability for potentially dangerous or expensive situations,” Beckler says.

A larger issue

Modesto’s basemap dilemma points to an issue affecting cities, counties and states: the importance of accuracy for resource accounting, modeling, analysis, science-based planning and informed decision-making. Many GIS continue to use mapping-grade or real-time differential (RTD) accuracy — which is submeter or subfoot (30 cm) — for much of the geospatial data. However, a growing number of applications require survey-grade or real-time kinematic (RTK) accuracy — which is centimeter or better — leading some users to establish new layers or upgrade existing GIS layers with RTK GPS accuracy.

The drive to higher accuracy comes from a variety of forces, including government regulations requiring accurate asset accounting; legal requirements for land titles or property boundaries; GIS applications such as modeling and parcel or tax databases; and new GPS technology that makes gaining high-accuracy data more cost-effective. Today, local and state governments often have a GIS made up of both accuracy levels: mapping grade, where accuracy is not critical, such as locating visible assets like hydrants or trees, and survey grade for parcel boundaries and other assets requiring centimeter accuracy.

Data community

In 1997, New Year’s Day in Washoe County, Nev., began with floods, which caused damages estimated between $167 million and $619 million — the most costly in the area’s history. To help repair the damage, the need for accurate and available geospatial information became obvious and critical. To Washoe County Surveyor Jack Holmes, the floods were a literal watershed in the county’s approach to what is now a standard-setting drive toward a “data community” involving high-accuracy GIS data, data exchange agreements across jurisdictions and a vision that includes a larger regional data community.

“All the emergency response teams wanted maps, but there was no common mapping system,” Holmes says. The available maps were patched together with differing scales and accuracy. County administrators realized their disaster assistance agencies needed maps of their jurisdictions or maps that accurately aligned with neighboring jurisdictions. As a result, three jurisdictions — Reno, Sparks and Washoe County — formed the Regional Basemap Committee in 1998. The group, which later added Reno, Nev.-based Sierra Pacific Power, spearheaded an overhaul of the county’s 20-year-old GIS, upgrading it to survey-grade accuracy. The committee also established a regional RTK GPS network covering approximately 1,200 square miles in northwestern Nevada.

The network, which uses virtual reference station (VRS) technology from Sunnyvale, Calif.-based Trimble, and includes seven reference stations, significantly reduces high-accuracy GPS field data collection costs to network users, without additional base stations. By eliminating base stations, VRS networks reduce user set-up time and personnel, although, in some cases, users leave someone to watch the base station. In addition, VRS networks expand a network area using fewer reference stations, improve data quality control and minimize the training for those with little high-accuracy surveying experience.

The network began operating in 2003, is free to the entire community, and is expanding at no cost to taxpayers. However, a technical committee charges a fee to check new maps developed in the region. The Nevada Department of Transportation is installing reference stations to tie into the system, and Holmes anticipates doubling the network area by the end of this year.

With the inter-jurisdictional agreements, all GIS data is on the same basis and coordinate system, and is shared freely between jurisdictions. “High-accuracy has allowed us to cooperate and exchange GIS data,” Holmes says. “We’re now all on the same page geospatially and are bringing other counties and cities onto the same page. We’re even going back historically and modifying all recorded maps to our current system.”

While Holmes and others developed Washoe County’s geospatial strategy, senior staff and elected officials have supported the approach, says County Manager Katy Singlaub. “Because we have this level of data sophistication and precision, we can address jurisdictional concerns with a high degree of accuracy,” she says. “The critical policy questions of who is affected by a policy decision, and what the impacts on those residents will be, all become more meaningful with accurate geospatial data.”

Singlaub sees the online zoning, land, census and utility data helping the region balance its planning as well as market itself for development. In fact, the development community frequently uses the system, Holmes says. “Our GIS network and parcel database is highly accurate. It’s common to have less than two centimeter accuracy between two different firms if they’re working on projects that share a common property line.”

On New Year’s Day 2006, the region faced a potential flood, and they were ready, using the GIS data to predict potential flood areas, expected flood levels and first-response areas. “We had all the maps we needed, including flood plains, contours, structures and maintenance needs,” Holmes says. “When the emergency came, everyone was dancing at how prepared we were.”

Accessing a state network

In 2004, Ohio’s Department of Transportation (ODOT) was the nation’s first agency to implement a statewide VRS network. Using 52 RTK GPS reference stations, it covers the 44,828-square-mile state and is available to all users. “The VRS system provides significant day-to-day benefits as well as cost savings for ODOT, consultants, construction work, GIS and related positioning applications,” says John Ray, administrator for ODOT’s Office of Aerial Engineering.

In fact, using the VRS network has been shown to provide a 15 to 20 percent increase in productivity, equipment cost reduction of 33 percent and personnel cost reduction of 18 percent — an overall potential project savings of 25 percent — in Warren County, Ohio, one of the first to benefit from the new ODOT network. One of the fastest-growing counties in the nation, the county was implementing a high-accuracy GIS for its Water and Sewer Department using its own RTK GPS base station and rover before the ODOT VRS system came on line. For the last part of the county’s GIS data collection project, it used the VRS network and will continue to access it to update its GIS data.

“We discussed using mapping-grade GPS data but were told the precision with RTK was much better, and we wanted a high degree of accuracy,” says Laura Gray, system data manager for the Water and Sewer Department. “We also wanted the elevation data that only RTK GPS can provide.”

That accuracy allows the department, for example, to more precisely locate valves when a water main breaks. It also provides GIS elevation data that enables modeling and other engineering applications. “We’ve really only begun to access the capabilities of our GIS,” Gray says. “As we continue to inventory our water and sanitary sewer utilities, our GIS will become a more integral part of our operations and planning.”

The Water and Sewer GIS is also affecting the county GIS. A decade earlier, it was developed from 18 volumes of paper parcel basemaps, according to Dawn Johnson, Warren County GIS Coordinator. Gray and her assistant Susanne Mason collect high-accuracy GPS data for newer subdivisions in a pilot study to compare the accuracy of county digitized data with the Water and Sewer RTK GPS data.

“With the GPS data, we know within plus or minus three centimeters where a subdivision corner is,” Johnson says. “We’re seeing shifts in our GIS as much as 12 feet in some extreme cases.”

For the future, the Warren County GIS Steering Committee is considering whether it is worth the enormous effort required to shift the existing parcel dataset. “Right now, I’m taking advantage of the high-accuracy data Laura and Susanne collect,” Johnson says. “But the Engineer’s Office and my department already have plans to acquire GPS equipment for expanded data collection.”

And her advice for any county converting its GIS data? “Have access to high-accuracy GPS equipment, [and] use it early in the process.”

Krista Stevens is a freelance writer in Los Altos, Calif.