reshape buffesr to avoid and reflect excluded areas?

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05-23-2012 10:08 AM
JohnSobetzer
Frequent Contributor
We need to create buffers around various polygons, but non-forested polygons cannot be a part of the buffers.  This is not a simple erase problem; the buffer needs to be "expanded" to avoid any NF polygons within it, treating them in a sense as if they were space that didn't exist, to get the required buffer distance in forested areas.  Normally this buffer reshaping is easily understood but manually intensive, a one by one process with a considerable subjective component and some trial and error, as additions are made to the outer edge of the buffer approximating the excluded shape, such that imagined lines running perpendicular from the outer edge of the buffered polygon would roughly go through the same length of feet of forested polygons as the buffer distance.

These NF polygons may abut the buffered polygons but more likely they don't, they may occupy just a portion of the buffer, their shapes are often quite irregular, and they often extend outside the initial buffer to create areas that can't be expanded into either.  At least we don't have to factor in 3D.  The buffers do need to have attributes that link them to the buffered polygons.  We have ArcInfo and Spatial Analyst.

An automated and repeatable "objective" process that worked pretty well would be preferable.  After looking at a discussion of how Maplex places labels by looking for "white space" outside features with a higher weight or labels of a higher priority, I wondered if a buffering process could be created that would avoid excluded areas.  To my quite limited abilities this seems darn near impossible, but I've seen some answers on this Forum and Stack Exchange that have solved other issues I couldn't grasp either, so I'll ask.
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LornaMurison
Occasional Contributor
Do you think you could post a screen shot to make your problem a little easier to understand? I'm not sure I'm following you 100%...
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JohnSobetzer
Frequent Contributor
I should have thought to add a visual example.  Thanks for asking.

I'll attach a rather straightforward version of the problem that doesn't involve any interaction with other buffer polygons.

These additions to the buffer area have typically been done by eyeball, then checked for distance.  In this case I ran an Identity of the buffers with the NF, (which is needed to get acres since there is also an acres consideration), exported the overlaps to a temporary shapefile, moved them to the edge of the buffer, cut them a bit, and then used the construct features tool (taking into consideration existing polygons option in 9.3.1) to add them to the buffer.
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LornaMurison
Occasional Contributor
My initial suggestion was going to be to take all of the NF polygons that fall within the regular buffer and merge them with the feature that you are buffering.  Then do a buffer on the whole thing.  That would work for the ones where the NF polygon is adjacent to the polygon that you want to buffer.  But in the case of the one that is just sort of floating within the buffer, the buffer might end up being too large...
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JohnSobetzer
Frequent Contributor
I like the suggestion.  It is one of the options I've considered and tested, and it should work well with NF polygons that are adjacent and rather "compact" in shape. It does have the problem you recognized, however, where it overlaps in the middle or outer parts of the buffer, and/or if the NF area has long and/or oddly shaped extensions, particularly if they extend outside the buffer quite a bit.  It requires a bit of prep work too to select and choose the merged items, and perhaps cut them up.   Still, it might be a part of a semi automated approach depending on how many situations fit its requirement.  Thanks.
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