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Home - General / All posts - calculate servitude area percentages of a buffer zone for individual landowners
MarcSt2 post(s)
#09-Jan-17 12:00

Hi all - I need to calculate area percentages where a powerline and the associated buffer zones cross individual landowners properties. Could anyone assist with a methodology to do this/ or point me at a relevant help topic? Ideally I need to automate the operation as the areas are quite extensive. (Manifold 8)

brgds and thank you in advance.

mechalas

838 post(s)
#14-Jan-17 17:04

Here's one way to do it that is pretty easy, though SQL could automate it further.

  1. Make sure your powerline is in a separate drawing and create a buffer around it. Or put the buffer in a separate drawing. Doesn't matter how you do this really, just make sure that you have a drawing where the only "area" object in it is the buffer around your powerline.
  2. Make sure the transfer rules for your property drawing are set. Presumably, each property has a taxlot ID number or some other unique identifier. Set the transfer rules on that column to "Copy" for "1 to N" and to "Sample" for "N to 1" (we won't need the latter, but you have to set it to something). This will ensure the column doesn't get zero'd out when you transform the drawing. I'll assume this is a taxlot ID.
  3. Now, duplicate the property drawing. Rename this to "Overlap".
  4. Create a map component. Add to that map the "overlap" drawing and your buffer.
  5. Use the transform toolbar to create intersections: [All objects in Overlap] Clip with (intersect) [All objects in Buffer]
  6. You now have little areas where the buffers and the properties overlap. If your transfer rules were set up properly, these areas should still have their original taxlot IDs (or what ever unique identifier was set up for them).
  7. Now, the unintuitive part. Property lines aren't perfect rectangles so you might have L- or U- shaped properties where the buffer intersects the property multiple times. You need to group these discontinuous areas by taxlot ID. Go to "Drawing -> Dissolve" and select the taxlot ID column. Your little intersection areas are now multi-branched areas (grouped by taxlot ID).

Now you have a drawing called Overlap with just the overlap portions, and your original drawing of the properties. There are a number of ways you can get area percentages from this. You can use SQL to join the two drawings on taxlot ID and divide the area of "Overlap" by the area of the original property column. Or you can open the "Overlap" table and create a relationship between it and the original property table on the taxlot ID column, then create an active column to divide the two areas. I think the SQL approach is better.

Something like this:

SELECT 

 O.LotID,

 O.[Area (I)]/L.[Area (I)]*100

FROM 

 [Overlap Drawing] AS O

INNER JOIN [Lots Drawing] AS L ON O.LotID=L.LotID

 

See attached.

Attachments:
powerlinebuffers.map

MarcSt2 post(s)
#17-Jan-17 11:23

Many thanks - worked 100%. I utilised the SQL method for future ease of use and automation.

Again thanks for your input and clear details / I have learnt something new and extremely useful.

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