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I have a point layer of 400,000 voter residencies and a point layer of 500 polling places. I am trying to find the average distance it takes voters to get to their polling location. Distance by road would be optimal, but I would settle for as the crow flies as well. I have ArcGIS Basic with Network Analyst. I just got NA last week, so I have no experience with it. I have a related field that can match individual voters to a polling location.

I appreciate any ideas. Thanks!

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Do you have a table matching residences with polling place? – whuber Jun 18 '13 at 15:28
I could easily make one. I have a polling place ID number for each residence in the residences attributes table. I also have that ID number for each polling place in the polling place attribute table. – brillo898 Jun 18 '13 at 16:31
Is it ok if the crow is named Jim? – Kirk Kuykendall Jun 19 '13 at 18:35
Have you looked at Location Allocation analysis? – Kirk Kuykendall Jun 19 '13 at 18:40
up vote 5 down vote accepted

The Euclidean distance calculation is easy: in the residence and poll layers compute [x] and [y] coordinates in a suitable projected coordinate system. Join each layer's attribute tables to an editable table that matches residences with polling places. (This could be the same as the residence table itself if you like, but often it's safer to use a separate table for the analysis so you don't inadvertently change your original data.) Use the Field Calculator to apply the Pythagorean Theorem in the form

sqrt((residence.x - poll.x)^2 + (residence.y - poll.y)^2)

The exact syntax will depend on the details of the join, what the field names are, what version of ArcGIS you are using, and whether you are working in VBA or Python.

After that calculation is complete, a summarize operation will compute statistics such as overall average distance, average per polling location, etc.

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It seems so obvious now! Thanks for your help, whuber. This is a great source for answers. – brillo898 Jun 19 '13 at 20:43

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