Creating a Travel Distance
I am trying to create a 20 minute travel distance zone on a standard Census tract shapefile Any suggestions as to how I might get started using 9.2.
Mapping Center Answer:
First, you don't produce travel distances directly from a census tract shapefile. You'd need a road network dataset (not just a shapefile, but something that contains weightings for speed limits, impedences for traffic lights, and stop signs, etc., and potentially additional time of day impedence weightings). Most network analysis software has a drive time buffer function that will create or select the lines in the network dataset that are within a given drive-time of a point you enter. You can then use that selection or set of lines to select census tracts--I would calculate a new field on the census tract to indicate that the tracts are within a drive-time of X for point Z. That would allow you to code multiple drivetimes and locations into the same census tract dataset--making the demographic analysis (that I would expect somebody might do later) easier.
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