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| GeoCommunity Mailing List |
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| Subject: | Re: [gislist] Assistance Please |
| Date: |
11/30/2005 02:15:01 PM |
| From: |
Quantitative Decisions |
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At 01:30 PM 11/30/2005 -0500, DuBose Griffin wrote:
>I have a shapefile (#1) of polygons with each
>polygon being a buffer around a bird's nest (n = 400). I have a second
>polygon shapefile (#2) consisting of individual polygons (n = 28000)
>with different areas (this is already calculated in square meters).
>What I want to do is select and combine all the polygons in shapefile #2
>within buffer 1 (#1) into a separate shapefile so that I can add up the
>area. Then repeat this for buffer 2 and so on.
>
>Another issue is that many of the buffers overlap.
A fast, easy way (regardless of what software you use) is to represent
shapefile #2 as an indicator grid of 1's in the polygon cells and 0's
elsewhere. Compute a circular neighborhood mean of this grid and then
multiply the results by the area of the circle. (Use your buffer distance
for the neighborhood radius.) Finally, extract the values of that grid at
each one of the bird nest locations. There's no problem with buffer
overlap--you don't even need the buffers.
--Bill Huber
Quantitative Decisions
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