Module 3- Special Topics in GIS - Determining Quality of Road Networks: Completeness

Map depicting relative completeness of two road networks

In this week's lab, we explored a method of comparing the completeness of two road networks covering the same area, in this case, Jackson County, Oregon.  The two networks to be compared are the U.S. Census Bureau's TIGER lines for 2000, and the Street Center Lines network from the Jackson County GIS Department.

First, we can simply compare the total length of all streets from the two networks, within the county.

A more rigorous method can show the pattern of relative completeness between the two networks. In this exercise, we overlaid the two road networks with a simple grid.  Then, by using ArcMap 10.2 Intersect and Summary Statistics tools, we were able to create a total length of road segments for each separate grid cell,  This procedure was carried out for both networks. Then, for each individual cell, the percent difference in road segment length between the two networks was calculated.  The following calculation was carried out on each grid:

(Total segment length of Street Centerlines) - (Total segment length of TIGER lines) 
                                     Total segment length of Street Centerlines                                     X 100

The result is negative percentage values in grid cells with larger TIGER line segment lengths, and positive values for cells in which Street Center Lines have a larger sum of segments.

Based on this method of analysis, TIGER Lines is more complete than the Street Center Lines, with a more cells with longer segment length.

The completeness results are depicted in the map above.  Blue cells are those in which TIGER Lines are more complete, and green cells are those in which Street Center Lines are more complete. (Darker tones represent higher percentage of difference.) The pale cells are those in which the lengths are very similar, within 3%, plus or minus.