A pilot project for landbase migration
Jay Clark
Product Manager, Utilities
Geographic Data Technology, Inc.
11 Lafayette St
Lebanon NH 03766
Telephone: 800 331-7881 ext. 1112
Fax: 603 653-0249
Email: jay_clark@gdt1.com
Abstract
This presentation examines data modeling, topological maintenance, and alignment of multiple spatial data
sets in a project for Atlanta Gas Light Company. Processes include:
- conflation of public vector data with Geographic DataTechnology’s addressed street centerline
- horizontal realignment of the resulting street network using aerial imagery
- auto-correlation of AGL’s street centerline to the improved landbase
- repositioning of AGL’s boundaries, point data, facilities and other data layers to the improved
geometry.
Introduction
This presentation discusses a pilot project undertaken by Geographic Data Technology, Inc. (GDT) for
Atlanta Gas Light Company (AGL), the eighth largest natural gas distribution utility in the United States.
Faced with advances in software and GIS technology since the development of their last GIS, AGL decided
that it was time both to replace their GIS software environment and to migrate to a more accurate and up-to-
date landbase.
When GDT met with AGL in January 2001, discussions of the landbase migration process centered on
three key issues.
Data quality
AGL wanted the new landbase to be spatially accurate enough to overlay an aerial image of equal or better
quality than a United States Geodetic Survey digital orthorectified quarter quadrangle (USGS DOQQ). This
would result in assumed horizontal accuracy of +/- 5 to 7 meters from “groundtruth”. AGL also stipulated
that attribution available with the data needed to be current and complete enough for outage management,
service request, and Customer Information System (CIS) purposes.
Management of facilities data conversion
AGL wanted to manage the migration of their facilities data to the new landbase in the most accurate and
efficient manner possible
Cost
AGL sought to balance the appropriate level of effort to get the job done correctly with a moderate budget.
It was decided to embark on a pilot project for DeKalb County, Georgia, in order to demonstrate the
feasibility of a solution from a commercial vendor such as GDT. DeKalb is one of the heavily urbanized
counties that make up the metropolitan Atlanta region.
The new landbase data
Quality Criteria
The following criteria were developed for the new landbase GIS:
- horizontal errors would be less than 7 meters averaged over 90% of all points in the data set
- sufficient attributes would be included to provide GIS functionality for all departments
- the GIS would employ a“real world” coordinate system
- it would be compatible with an “off the shelf” relational database management system (RDBMS)
- 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
