Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Intersecting Route Events

Just as you could combine a set of polygons with another set of polygons to create a third set of polygons with appropriate (geo)graphic and attribute information, you can also combine the graphic and linearly referenced attributes of routes.

Suppose that someone suggests that there is a correlation between auto accidents and road conditions on Route 30000030: if the Rating is less than 75 on a section of the road the number of accidents (per mile) is greater. To test this, you want to combine the accident data with road condition data.

____ 21. If necessary, start ArcMap with Pittsburgh_Routes, as saved in the previous step.

____ 22. Open the attribute table of Some_Routes. What is the Shape_Length of 30000030 to one decimal place? ____________ feet. Close the table. Under Selection, clear any selected features and records.

The length of a route, considered as a feature, is, of course, in the units of the coordinate system. However, as noted previously, the event measures are in miles. Just for the sake of confidence, let’s compare one against the other.

____ 23. Restore the attribute table of Pavement Events. Select the records where Route1 is 30000030. Display Selected Records.

Nowhere in the table is the length of each segment, but we can fix that, since we have the beginning and ending mile point number. With this few records (six), you could easily verify that there are no overlaps (a requirement for valid segmented data) and determine ...