GIS5935 - Lab 3 - Determining Quality of Road Networks - Completeness

In Lab 3, the second part of our analysis of road network quality, we focused on completeness of the networks.  Our task was to provide a comparison between street centerline roads and TIGER 2000 roads for Jackson County, Oregon.  We were provided a county boundary layer as well as a grid of 5km by 5km polygons to overlay the roads for analysis.  A simple method of measuring completeness assumes more length means more complete.  We reported the total length for each road network for the entire county.   The TIGER network contained more total length than the centerlines and therefore was more complete.  However, our assigned reading by P.A. Zandbergen, et. al. explains the brief history and the positional accuracy issues with the TIGER 2000 dataset.

Determining the completeness for each polygon grid was obtained by breaking up the road segments using the polygon boundaries and determining the length of each road segment contained inside each respective boundary.  Using the Summarize option within the attribute table I was able to create a table containing the segment count for each grid and the total length of all the segments within each grid.   By subtracting the TIGER road length sum from the Centerline road length sum for each grid I was able to determine which road segment was more complete per grid.  The TIGER network was more complete than the Centerline network in 162 out of 297 grids.   The Centerline network was more complete than the TIGER network in 134 of the 297 grids.  One grid polygon did not contain any road segments.  After calculating the % difference in network length, I was able to create this choropleth map depicting road network completeness.  Difference values that were positive percentages meant that the Centerline network was more complete.  Polygons with negative percentages meant that the TIGER network was more complete.  Using completeness in conjunction with the positional accuracy analysis we performed in last week's lab aids the end user in determining the quality of the road network.

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Completeness of Road Networks - A Comparison Between TIGER Roads and Jackson County, Oregon Centerlines