Calcite | Level 5

## How to calculate ZCTA radius?

Purpose: How to calculate the ZCTA radius within a ZCTA?

Background: I have two groups of nodes: from and to. The two groups may locate in the same ZCTA (25%) but most of them had different ZCTAs (75%). I managed to calculate the ZCTAs distance for the 75%, centroid to centroid. But I don't know how to assign a distance to the other 25%. I expect to use ZCTA radius as a proxy for that purpose. Can anyone help me with it? Thank you in advance!

BTW, 5-digit zip code is the only available geographic info.

3 REPLIES 3
Lapis Lazuli | Level 10

## Re: How to calculate ZCTA radius?

You can find a ZCTA table with square mileage A (area) for each ZCTA, see this website http://proximityone.com/cen2010_zcta_dp.htm.

Based on this table you can calculate a ZCTA radius R from A=πR2, then R=(A/π)1/2.

You can also look into getting an average distance between two points within a circle, see

https://math.stackexchange.com/questions/135766/average-distance-between-two-points-in-a-circular-di...

Hope this helps.

P.S. For some reason superscripted 2 and 1/2 came out as subscripted 2 and 1/2.

Calcite | Level 5

## Re: How to calculate ZCTA radius?

Leonid,

Thank you!

Is there any supporting evidence to treat a ZCTA as a circle to do that?

Kevin

Lapis Lazuli | Level 10

## Re: How to calculate ZCTA radius?

Hi Kevin, I was just answering your question "How to calculate ZCTA radius?" - What other than circle has a radius? 🙂

Lacking information about the ZCTA shape, circle seems as a reasonable approximation.

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