GIS4930 - Data Accuracy - Assessment of Road Network Data Completeness

In this lab, we examined road network completeness in Jackson County, Oregon, by comparing the locally maintained Street Centerlines to the US Census TIGER/Line (2000). The goal of the accuracy assessment was simple: measure how fully each dataset captures the real street network, not by point accuracy, but by total road length.

I projected TIGER to the centerlines’ projected CRS, then intersected each road layer with a 5×5 km grid so only the parts inside each cell counted and any segments crossing cell boundaries were split. After intersecting (when geometry changes), I recalculated segment lengths in kilometers, summarized the totals by grid cell for each dataset, and joined those totals back to the grid. To compare them, I computed a percent difference using Centerlines as the base: $\% \text{Diff} = \frac{\text{Centerlines} - \text{TIGER}}{\text{Centerlines}} \times 100$. Positive values mean Centerlines are more complete; negative values mean TIGER is more complete.

In short, a simple length-based metric provided a transparent way to evaluate completeness: TIGER was more complete overall by total length, but the grid map revealed many local areas where the county centerlines exceeded TIGER.