Elwyn McLachlan
Trimble Navigation Ltd
Abstract: As issues of accountability and liability become increasingly important in local government, ensuring that GIS databases are kept up-to-date and relevant is critical. This paper will illustrate how GPS-based data collection systems can be used to validate and update GIS data. Issues of data quality and reliability will be discussed. Relevant case studies both from within the US and internationally will be used to illustrate key points.
GIS technology has unquestionably revolutionized the way that local governments operate. Allowing massive amounts of data about properties, assets and incidents to be stored, managed and analyzed, has resulted in reduced operating costs and increased efficiencies. With government regulations, like the 1999 GASB-34 amendment, now requiring even closer tracking and reporting of the financial value of assets, GIS is again the savior. Under the GASB-34 amendment all state and local government agencies must report on the financial value of the assets they maintain. They can opt to do this by either depreciating the value of the asset by a set amount each year, or by tracking the condition of the asset on a regular basis. The latter method, commonly referred to as the "modified approach", is generally favored, as it allows the agency to maintain the value of the asset, thus providing more collateral when federal government funding is required for a project. To follow the modified approach, not only must the authority have an up-to-date inventory of their existing asset infrastructure, they must also monitor and record changes, removals and additions to keep the database current. GPS-based data collection and maintenance systems provide an effective solution to this problem.
GASB-34 requires reporting on the financial value of all public infrastructure assets, including street furniture, bridges, sewer and water systems, electric and gas utility infrastructure. A GPS-based data collection system offers an efficient and productive means of populating or updating a GIS database of such assets.
When faced with building a database of assets from the ground up, GPS provides accurate location information, and a system designed specifically for GIS data collection makes it possible to record detailed feature and attribute information. Most data collection systems allow the ability to define a data dictionary and a data structure that guides the field worker through collecting the correct information in the field. In the example of traffic infrastructure, this would ensure that the field worker documents exactly what devices are hanging from a traffic pole, such as stoplights, pedestrian signals, and signs. Using a data dictionary facilitates data collection to ensure that all of the necessary data is collected in the field, and that attributes are stored in a format that is compatible with the existing GIS database. Key information, such as the condition of the feature, can be flagged as a "required" field, forcing the field crew to make an assessment, rather than being able to leave it blank.
Some GPS-based data collection systems allow data from an existing GIS database to be uploaded and taken back into the field, where information simply needs to be validated and updated. With graphical map and navigation displays that show exactly where you are in relation to the assets of interest, these field systems allow easy relocation of features for inspection. Some systems can also create a "check-list" that will graphically display what features have already been visited, and what is left to do. "Date-visited" attribute values can be automatically generated, to store a log of when an asset was last inspected. This is crucial in meeting the GASB-34 requirements, where the condition of each asset must be re-assessed every three years.
Whether updating existing GIS data or building a new asset database, a GPS-based data collection system is a valuable tool. However capabilities of the system that ensure quality feature and attribute is collected in the field, vary widely. Quality control on both the feature information and on the GPS positions should not be overlooked.
Figure 1 Trimble GPS Pathfinder System used for a Stormwater Infrastructure Inventory
In May 2000 the US government made the decision to turn off the deliberate scrambling of the GPS signal known as Selective Availability (SA). As a result, the accuracy of the GPS system was improved from roughly 100 meters, to less than 20 meters. And in fact, ongoing testing and analysis has shown that we can typically expect less than 10-meter accuracy out of a typical GPS receiver. But, even with the improved accuracy provided by the GPS constellation, not all GPS is equal. Differential correction and averaging techniques allow us to remove some of the error still apparent in the GPS signal, resulting in higher quality, more consistent data. Without reliable differential processing and averaging procedures, data from different GPS receivers can vary widely.
When using a GPS-based system to populate a GIS database, it is important to track the quality of the positional information collected, as this can have a significant impact on the use of the data. If GIS data is used, for example, to determine the best route for a sewer inspector, and the data is only accurate to 10 meters, then the route output by the system may not be efficient, resulting in wasted time in the field. Including metadata in the GIS output gives an indication of the quality of the GPS position, along with the feature and position information.
In recent years there has been much talk about GIS as part of an enterprise system. The GASB-34 amendment has become a catalyst for this, as the reporting required by GASB-34 brings together asset information, typically stored in a GIS database, with financial data. Using the enterprise data together in this way not only provides more accurate financial reporting, it allows more efficient use, deployment and utilization of resources. An automated work-order-management system that had access to all of an agency's data can re-route a field maintenance worker to an urgent job in a timely manner; navigate the person exactly to the correct location; ensuring they have the correct tools and materials to fix the problem (and if not, route them past a depot to collect); track how much time they spend on the job for billing purposes; update the database records regarding the asset; and then route the worker to the next job. Happier customers when problems are promptly fixed, less wasted travel time for the field worker, and better tracking of financial resources over time, are just some of the advantages resulting from bringing data and associated technologies, such as GIS and GPS, together.
State and local government agencies have been quick to adopt GIS and GPS systems as a means to collect, store and manage asset information. However, the potential for these technologies as a seamlessly integrated part of the organization's operations, is just beginning to be realized. In the example above, all of the technology exists to make this possible, it is simply a matter of linking the information together in an integrated system. In the near future, with wireless connectivity, reduced cost of computing devices, and more powerful database systems becoming a reality, local government agencies will be able to further increase productivity and achieve significant savings, by leveraging enterprise data across all operations. Quite by coincidence, the GASB-34 requirements have become a driving force in bringing these technologies together.
Elwyn McLachlan
Business Development - Mapping & GIS Systems
Trimble Navigation Ltd
7403 Church Ranch Blvd, #100
Westminster, CO 80021
USA
Phone: 720 887 6100
Fax: 720 887 6101
Email: elwyn_mclachlan@trimble.com