How the west was mapped - The good, the bad and the ugly
Asset Recovery
Since most of the Water, Sanitary Sewer, and Gas systems lay underneath the ground,
unique methodologies were employed to recover and record features related to these
systems. NTUA field personnel from each of the District Offices were responsible for
locating these underground features. Some extraordinary measures were employed to
assure this. As an example, Gas locate crews many times had to ‘dig up’ lines due to the
fact that some older gas lines constructed of polyethylene did not have tracing wire.
Many times locating water lines required the excavation. While the pipelines and other
features were located by the NTUA, marker post and ‘whiskers’ were placed on the
ground in the proximity of the features to assist the crews in conducting GPS mapping.
In addition, while mapping water and sanitary sewer systems field crews utilized NTUA
As-Built maps. There were no As-Built maps and very few other reference maps for gas
to assist the crews in their field inventory mapping. NTUA personnel constructed
reference maps in the field utilizing 1 meter resolution aerial photos in conjunction with
locates to produce very useful maps for the crews.
Quality Assurance and Quality Control
Another unique feature of this project was the high level of Quality Control and Quality
Assurance. It is commonplace in the utility mapping industry to accept a field data
collection accuracy rate of 98%. At this rate, knowing that there were some 6,000,000
fields of data to be collected in this project, there would have been approximately
120,000 errors and omissions. The goal of the Quality Assurance/Quality Control
program in this project was to facilitate an accuracy rate of 99.5%. The field level
Quality Control/Quality Assurance measures in this project consisted of:
- FMGPS ™ field checks
- Arc-View ™ checks
- Total Fit ™ Topology checks
- Field Checks
In addition, M&M developed a complex set of QA/QC and conversion routines to verify
the validity of data collected in the field. These tests ensured that the data had complete
connectivity. They also ensured that data followed stringent connectivity rules. For
instance a single-phase secondary overhead conductor could not connect to a three-phase
overhead primary without a single-phase transformer present at the junction. Every
connectivity situation that had consistent rules was accounted for with all electric, gas,
water and waste water systems.
A second level of QA/QC was provided by Dog Creek™ Software. This was used to
ensure that field-collected data matched the attribute domains in the data model.
Therefore if a field contained a value outside of the list of acceptable list of valid values it
was reported in an error log.
This information and reports from the M&M tests was provided to the GPS contractor
who reviewed and corrected the source GPS shapefiles as needed. In many cases no real
problems existed. Questionable values were listed in logs to be scrutinized by
knowledgeable NTUA staff. In some cases – especially with electric system data- NTUA
engineers were not available to evaluate features shown in error logs, so an item was
added to the geodatabase with a code indicating which QA/QC test a feature did not pass.
About 70 types of errors were flagged. Over 1,000 features remain to be inspected, error
codes checked problems resolved.
Once the data was deemed satisfactory or when it was flagged, a second conversion
routine converted intermediate products into the next intermediate feature. These are
ArcInfo coverages for features like primary overhead electric lines or water system
valves. These features were then imported into the Oracle geodatabase with standard
ArcGIS™ tools.
