First I determined the total length of the two road networks using the attribute Statistics function for each road network shapefile. The total length of the Street Centerlines network was 10,873.3 km. The total length of the TIGER 2000 network was 11,382.7 km. Based on those numbers, the TIGER 2000 network is more complete.
The second part of the lab required me to determine the total length of roads within each polygon of a county grid of 297 polygons. I first had to split the lines into segments within each grid polygon so only those segments within each polygon would be counted toward the total per polygon. The Intersect tool took care of that step, with each segment now connected to it's particular grid. To get the total length for each grid polygon, I used the Summarize Statistics tool to create two tables, one per network, which I then joined to the grid shapefile. After some attribute field calculations to determine the difference between the two networks, I could then determine the comparitive completeness of the networks based on grid polygon count:
Street Centerlines more detailed than TIGER 2000: 41 polygons
TIGER 2000 more detailed than Street Centerlines: 255 polygons
Total polygons: 297 (one polygon contained no streets from either network)
To find a percentage of the differences in total length, I used the field calculator to divide the difference in total sums by the Street Centerlines total length, producing a range of values from -1739.7% - 100% difference across the grid polygons.
To find a percentage of the differences in total length, I used the field calculator to divide the difference in total sums by the Street Centerlines total length, producing a range of values from -1739.7% - 100% difference across the grid polygons.
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| Choropleth map showing the difference, by percentage, of the total length of roads within each grid for two road networks in Jackson County, OR. |
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