GIS Implementation

No single source existed from which a county’s road network could be digitized, so each county began with research across a wide variety of maps and imagery. Sources included Census TIGER line files for the road and boundary network, USDA aerial photography and soil-survey sheets, USGS 7.5-minute quadrangles and digital orthophoto quarter quads, DOT route records, and county and municipal maps. Aerial photography was selected from leaf-off, low-canopy periods of the year so that roads under tree cover could be seen. Each source carried its own scale, date, and accuracy; the research established which covered which parts of the county, which was most current, and how they disagreed, and produced a reconciled plan for digitizing so that every road was captured once, from the best available evidence, on a consistent coordinate framework.

Once a county’s basemap was complete, Mr. Parnell converted the linework into attributed entities, assigning elemental values to each roadway segment, intersection, and interchange as the inventory system defined them. In the 36 counties he produced, every attribute and GIS element was created manually and specifically by him rather than converted from an existing digital dataset: route identification and classification, the inventory fields the system required, and the linkage between each element’s geometry and its record, entered and checked element by element. The system’s coding — its data structure, software, and database — was the Department’s; his responsibility was populating that structure correctly for every element in his counties. Manual attribution at county scale was the largest single component of the work and the reason the engagement extended over years.

The engagement ran approximately seven years and delivered more than a third of the state’s county basemaps from one vendor. The scale of the network matters: North Carolina maintains the second-largest state highway system in the country, close behind Texas, because the state rather than the counties owns nearly all public roads outside municipalities, so each county basemap carried a dense inventory of state-maintained routes to document and convert into intelligent entities. Among the 36 counties was Mecklenburg, the most populous and most densely developed county in North Carolina, whose urban road and interchange network was the densest in the state to map and attribute. The program represents the largest sustained geospatial implementation in Mr. Parnell’s career and the foundation of the GIS, mapping, and attributed-network work recorded under GIS & Geospatial.