The Big Picture: The Heart of the TIGER
The U.S. Census Bureau is most well known for its decennial enumeration of citizens, but it’s also recognized within the geospatial industry as the developer/caretaker of nationwide GIS datasets. In the 1960s, the bureau developed a GIS called Dual Independent Map Encoding (DIME) to handle spatial data. This system was replaced in 1990 with the Topologically Integrated Geographic Encoding and Referencing (TIGER) database, which was linked to the Census Bureau’s Master Address File (MAF) and enabled geocoding of street addresses.
As both public and private industries have more frequently relied on the availability of such information and are continually enhancing the accuracy of their own data, the need to ensure the accuracy of the MAF/TIGER data has increased. In 2002, the Census Bureau embarked on an initiative to produce a highly accurate (7.6 meters or better) street centerline “digital map” (geographic data base) of the entire United States, Puerto Rico and the associated Island Areas. Called the MAF/TIGER Accuracy Improvement Project, or MTAIP, the project aimed to correctly locate every street and other map feature in the TIGER database as well as each MAF address and implement an effective automated feature change detection methodology. The Census Bureau’s Geography Division recognized that for the MTAIP initiative to achieve this goal, there was a crucial need for accurate geospatial control that could be used to perform qualitative assessments of current and future submitted datasets seeking inclusion into the bureau-maintained MAF/TIGER database.
To develop that control, the Census Bureau launched the Accurate Coordinate Datasets Collection (ACDC) project in 2005, led by Michael Baker Jr. Inc., a professional engineering and consulting services firm headquartered in Moon Township, Pa. The firm was chosen based on its proven capabilities, prior experience in related activities, its ability to handle shifting workloads, and its familiarity with the concepts, practices and procedures of collecting accurate street-intersection points for TIGER horizontal accuracy verification due to prior participation on the bureau’s MTAIP initiative. The objective was to provide spatially accurate ground control throughout the entire United States and U.S. territories for use in support of the Census Bureau’s MTAIP. However, the Census Bureau quickly came to rely on Baker for more than data. “Very soon after the beginning of the contract, we realized the added value in Baker’s selection as trusted advisors when predetermined procedures/requirements put forth by the Census Bureau presented certain issues in the field,” says J. David Bush, the bureau’s contracting officer’s technical representative (COTR). “In each case, Baker not only presented us with an issue, but they delivered alternative solutions from which to evaluate and consider.”
To aid each collector in the determination of viable intersections and to promote continuity/consistency between the team members, Baker developed unique data capture methodologies, techniques and standards that were demonstrated first-hand to the COTR during a week-long trial. Baker also developed and implemented standardized training programs for field safety, GPS equipment testing (performed at geodetic bench marks or monuments) and data collection. Staff training consisted of both classroom and field coursework and also entailed biannual “ride-alongs” by GPS supervisors to verify that the required process outlined in the task orders were being executed as directed.
By understanding the vital need for a nationwide dataset of accurate control points, Baker and the Census Bureau formed a working partnership that was well-equipped and capable to perform the largest such geospatial undertaking of its kind. During the four and a half years of field collections, the Baker team was issued 22 separate tasking orders and performed coordinate collections within 1,018 counties/municipalities spanning 37 states and five U.S. territories. Coordinates and observed road name attributions were captured to a horizontal accuracy of +/-1 meter at the center of “well-defined” photo-identifiable street intersections. All coordinate collections performed by Baker’s team were derived from GPS equipment coupled to Baker’s own GPS/GIS software, but Baker was also tasked to investigate each assigned collection area for alternative sources from which coordinates could be derived. These included public land surveys, cadastral data, aerial photography and satellite imagery. To determine the viability for accurate coordinate extraction, each potential data source was assessed for spatial accuracy, age, resolution, cloud cover (if applicable), availability, price and subject area coverage.
Upon navigating to a “well-defined” intersection, a collector would position the GPS antenna over the center point of the converging street segments and begin the collection sequence. The robust capabilities of GeoLink were again used to average a minimum of 75 GPS positions, facilitate the association of terrestrially observed attribution to the newly georeferenced locations, and automatically filter errant GPS readings that could degrade the accuracy of the derived point. The averaging and filtering functions were configured to ensure the highest and most repeatable level of positional accuracy, which routinely resulted in spatial locations 30 percent more accurate than those derived by GPS alone. To further enhance the collectors’ effectiveness, both audible and visual alarms were enabled to alert when GPS quality factors (number of satellites, signal strength, positional dilution of precision, velocity, acceleration, and real-time differential correction) were outside of acceptable tolerances.
To ensure each collection area comprised an acceptable spatial dispersion of control points while also focusing on point densities, intersecting road angles and road alignment curvatures, automated routines were developed to create a valid sampling of candidate intersections throughout the subject area. Using standard GIS analysis tools and point generation routines, the process began with the automated identification of all intersections throughout the subject area. Each generated candidate quality intersection point (QI point) was assigned a unique identification number (APID), which would serve as the unambiguous link between the submitted dataset and the GPS-derived coordinates supplied by Baker.
Baker relied on its team of GPS professionals and teaming members to make the final determination as to the quality of each intersections’ configuration based on real-world, field-observed information. To qualify as a viable collection, each intersection was assessed for the following:
• Centerlines of roads forming the intersection should meet at right angles (90 degrees +/- 16 degrees).
• The intersection must comprise only three three-way or four four-way intersection road segments; two-way or ≥5 intersecting road segment intersections would not be collected.
• There must be a clear view to the sky with no overhanging trees or tall buildings that could impede the reception of GPS signals or degrade the quality thereof.
• Roads should be constructed of a hard surface, such as asphalt or concrete, whenever possible.
• Selected intersections should have road names posted at the intersection.
• Selected intersections must not be composed of driveways.
After all collections within the subject area were completed, the field-captured data were transmitted to the data processing center in Baker’s Jackson, Miss., facility through Baker’s secure enhanced File Transfer Protocol (eFTP) site, where it was retrieved and placed through an arduous QA/QC regimen. These processes entailed the development of several custom-automated routines to assess, validate, bundle and deliver the final products.
Baker also developed a custom project management Web portal that facilitated secure and efficient data transfer and further enabled the Bureau’s COTR to access current production activities, documentation, deliverable postings and work package histories/reports. Operating within the boundaries of the work breakdown structure, the client was never more than a few keystrokes from directly assessing the status of each work package or the project as a whole.
As with most collection area taskings, the Census Bureau had already been presented a locally or commercially supplied dataset seeking inclusion into the MAF/TIGER database, for which quality control points were needed to assess the submission. As part of Baker’s cost-saving initiative, the firm was able to regularly group collection areas to minimize mobilization costs and further perform coordinate collections for areas in preparation for future submitted datasets, which would eliminate unnecessary downstream expenditures.
Within each collection area, Baker was tasked with collecting 110 quality control points at or near the identified SSI locations. To exceed these requirements and ensure the viability of the supplied data for years to come, Baker captured an additional 10 to 20 percent within each subject area. SSI point locations were always assessed for collection first; however, on average, 25 percent of captured intersections were selected from the list of candidate QI points due to local conditions that were not favorable for the accurate collection of the original SSI point.
Baker provided consistent and standardized deliverables throughout the life of the project that yielded a 99.6 percent first-time acceptance rate. The firm completed the entire program ahead of schedule and $2.4 million under the budgeted allocation. What’s more, due to the delivery of high-level positional accuracies on generated control points (+/-1 meter) as compared to the spatial accuracy requirement for acceptance into the MAF/TIGER database (≤7.62 meters), Baker has ensured that the supplied control coordinates will be valid for use by the Census Bureau for years to come, even as it continues to enhance the spatial accuracy of its nationwide datasets.
“Baker met every one of the Census Bureau’s technical expectations,” notes Bush. “The quality and timeliness of their work exceeded our expectations, and the value of their management on this project truly spoiled us. They set standards to which we still refer in appreciation.”
Baker was selected as the Grand Award winner in the 4th Annual MAPPS Geospatial Products and Services Excellence Awards for its work on the ACDC project. For more information about Baker, visit www.mbakercorp.com. Additional information about MAPPS and the Geospatial Excellence Awards can be found at www.mapps.org.