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Track: Federal Systems
David Hansen
US Bureau of Reclamation
2800 Cottage Way
Sacramento, CA 95825-1898
Telephone: 916-979-2418
Fax: 916-979-2505
E-mail: dhansen@mpgis7.mp.usbr.gov
Coordinate Accuracy Reporting for Geospatial Data Sets of Mixed Lineage
Defining Issue: At a session in the 1996 Esri User Conference, considerable discussion developed over the estimation and reporting of coordinate accuracy for GIS data sets. The Content Standards for Geospatial Metadata by the Federal Geographic Data Committee (FGDC) require an estimate of coordinate accuracy as part of the documentation of GIS data sets. This paper is submitted to further the discussion on methods for estimating, managing, and reporting coordinate accuracy. GIS Solution: Increasingly, geospatial data sets are being developed that contain features captured with different spatial resolutions. Some features may have highly accurate GPS coordinate values or other survey control. Other features have coordinate values that are much less certain. Even where all coordinate information of a data set is developed from a single source, the coordinate location of some features is better known than for other features. For the long-term maintenance of these data sets, this information should be
managed as a portion of the data set. There are a variety of ways that this has been done, but at present there is no generally accepted guide or method. The FGDC standards provide for a report on the accuracy assessment of the coordinates. However, this report is a general assessment of the coordinate accuracy of the data set. The standards do not address feature-level reporting of coordinate accuracy. Methodology: As a focus for this discussion, the development of a digital data set will be presented where features were initially captured from aerial photography and then coordinate values for some features were updated using controlled GPS information. These features represent linear features carried as arcs where the GPS control represents the intersection of the arcs in a network. The point locations of the intersections represent one level of coordinate control for the overall coverage. A separate level of accuracy can be assigned to these points. The method of storage and retrieval of this
information will be presented.
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