- SPECIAL REPORTS
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Inaccurate documentation of property boundaries poses many problems for local governments in the United States. Spatial inaccuracies within a land base can lead to the inadvertent placing of utilities or other publicly owned facilities on private property when originally intended for placement in a right-of-way. Moreover, erroneous parcel information can often lead to disputes over property lines.
The City of Jacksonville Beach in northeast Florida experienced some of these challenges. Large numbers of parcel boundaries and right-of-way lines did not correspond to their known dimensions or locations, and these discrepancies prevented the city from providing a variety of public services with a high level of confidence and precision. “Without accurate parcel and right-of-way information, the city couldn’t move forward with its infrastructure projects on a timely basis,” explains Donald F. Terrell, senior network/GIS administrator for the City of Jacksonville Beach Information Technology Division. “A more-precise land base would allow us to leverage this information among multiple city departments and introduce new applications and improved services.”
Data Cleanup and Field CollectionPrior to building the cadastral fabric, the team first performed a massive cleanup effort on the existing parcel data. The most common data issues involved pseudo nodes, overshoots, undershoots and densified arcs. Pseudo nodes are arbitrary nodes located along the parcel vertices, which split parcel lines into multiple segments. Without correcting pseudo nodes, the dimensions would be split between segments causing multidirectional distortions in the parcel shapes. Undershoots occur when the parcel line is too short, which leaves a gap, while overshoots occur when the parcel line is too long, which leaves a dangling node.
To ensure accuracy, the team relied on recent survey data gathered from a roadway project in Jacksonville Beach. Because the data sets--specifically the corner points--were stored in a centralized GIS database at RS&H, new surveys were not required for this project.
Concurrent to the data cleanup effort, the team collected GPS bench marks, monuments and known locations of points, such as manholes, fire hydrants and light poles, from high-resolution aerial photography provided by the city. Using this information, the team created a 14-section grid dividing the project at major roadways. The team collected points using a Trimble GeoXH GPS unit coupled with a Zepher antenna, which provided submeter horizontal accuracy. These points were then post-processed prior to incorporating them into the fabric to ensure subfoot horizontal accuracy.
Parcel RectificationOnce the clean data and control points were built into the cadastral fabric, the team began parcel rectification. With nearly 15,000 parcels to rectify, RS&H designed a workflow that maintained the 14 grid sections and created a separate fabric for each one. This step streamlined the quality control and assurance process.
At the project’s onset, the team set a 5-foot tolerance on the parcels and also identified three status categories: in progress, review and historical. In-progress parcels were those that still needed to be edited, while review parcels were those that had been edited but did not fall within the 5-foot tolerance or were missing dimensions. The historical parcels were edited and were within the 5-foot tolerance. The initial analysis of the data involved identifying parcels that exhibited the correct dimensions and marking them as historical. Parcels in the review category were plotted on an aerial background and given to the city for final approval or direction for further correction.
While rectifying the parcels, the team used high-resolution aerial photography as the base layer to ensure proper placement of city blocks after they were disconnected and edited. It was extremely important to maintain and correct right-of-way information when reconnecting the parcel blocks. The accuracy of parcel corner points and dimensions was maintained within 5 feet.
A Proven SuccessThe cadastral data management tools allowed the city and RS&H to create a topologically integrated geodatabase, or cadastral fabric, made up of lines, line points, points and polygons that represent each parcel layer. Once the existing parcel data sets were integrated into the cadastral fabric, new fields were generated by the software containing the dimensions of each parcel segment. These dimensions were then compared to known dimensions collected in the field and corrected using Cadastral Editor coordinate geometry (COGO)-based data entry capabilities.
The City of Jacksonville Beach’s land base upgrade is now benefiting the city’s public safety and planning initiatives in a variety of ways. For example, the police department is using the new information to create more-accurate maps for its emergency dispatch units and computerized Enhanced 911 emergency services system. These improvements are possible due to the more-accurate right-of-way data set, which allows the creation of a more-precise street center line shapefile used in the geocoding process. In addition, the improved land base is being used by the city’s planning and development, public works, and electric departments to make better decisions regarding the location and placement of utilities as well as to better manage the city’s assets.
“The new land base gives us more control over what infrastructure is out there and how it’s working,” Terrell explains. “Now our staff can make better decisions more quickly and with much more confidence.”
For RS&H, the project is expected to generate new opportunities in creating and maintaining cadastral data as other cities and counties seek ways to improve land base accuracy and infrastructure control.