A Pilot Project for Land base Migration
Quality Criteria
The following criteria were developed for the new landbase GIS:
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Horizontal errors would be less than 7 meters averaged over 90% of all points in the data set
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Sufficient attributes would be included in the new landbase to provide GIS functionality for all
departments
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The GIS would employ a “real world” coordinate system
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It would be compatible with an “off the shelf” relational database management system (RDBMS)
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The system would accept transactional updates.
Data Specifications
Spatial accuracy within the tolerance stated would be obtained using digital vector data from the Georgia
State Data Clearinghouse, or, where vectors were unavailable, created from USGS DOQQ.
The following data model was selected.
Landbase GIS Transportation Data Model
It was agreed that grouping of objects and attributes would support all departments in AGL
It was also decided that data delivery would be in Geographic projection, using NAD83 and decimal
degrees. For purposes of the pilot project, the data would also be published in UTM zone 16, NAD83, in
meters. This would allow the data to be overlaid onto USGS DOQQs for a spatial “sanity check”.
For purposes of the pilot project, ArcView® GIS format was used to display the data. For full rollout the
data delivery would be in the form of a Geodatabase or ArcSDE™ files. Specific RDBMS was not
determined at this time at the outset of the project
Conflation
(Alan Witmer, 2001)
GDT acquired the DeKalb County GIS coverage from GSDC and conflated the horizontal control network
into its core database. The process of the vector conflation activity is described below. GDT’s approach
was to modularize the software and the process for each step listed below, allowing for individual
development, tuning, independent operation, and quality assurance.
Correlating features in two landbases (conflation) requires these steps:
Prepare the databases for conflation processing.
Analyze the incoming data’s quality and usability, and convert as necessary to a common format.
