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I have population data matched with polygons and a set of points that I have drawn buffers around. Assuming that the population within each geographical area, i.e. the polygons, is evenly distributed, how do I calculate the population within each buffer in ArcGIS? Some of the buffers are overlapping.

If you need I could send you the data.

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  • This is sometimes called areal allocation. I have a description of doing it in another answer (I'm sure there are others floating around this site as well.) – Andy W Mar 5 '15 at 18:28
  • It's also known as apportionment, and this specific method is apportion by area. I discuss some of the implications and link to discussions on alternative methods in my answer at gis.stackexchange.com/questions/104219 Also related, for QGIS (but only in the tool used to summarize), is gis.stackexchange.com/questions/133832 – Chris W Mar 6 '15 at 2:05
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This can be accomplished with an Intersect, followed by a Field Calculate, and then finally a Summary Statistics. Make sure that your buffer feature class has a unique ID field.

Before getting started, you will need to add a field (name Polygon_Areas, type Double) to your population polygon feature class, and then field calculate it, using Shape_Area as the input. This will create a field with your areas that can be carried over in geoprocessing.

Add area to field

Now perform an intersect with your population polygons and your buffers as inputs.

Intersect

A new feature class is created. Add a new field to it - maybe Area_Pop, type Double.

Field Calculate this new field in your intersect feature class:

Population field * (Shape_Area / Polygon_Areas)

Calculate population

Finally, you can perform a summary statistics on your intersect feature class. Use the Area_Pop as your statistics field and chose SUM as your type. Add the unique ID field for your buffer feature class as your Case field.

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Voila. You can perform a Tabular Join from your new table back to your original buffer feature class and add the SUM_Area_Pop field to a new field with a field calculate.

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Good luck!

  • if the population layer is raster, do you know how to do it ? – toby Mar 5 '15 at 19:49
  • You're welcome. I'm a vector guy; raster's not my bag I'm afraid. – Emil Brundage Mar 5 '15 at 19:51
  • Without running through a test I'm unsure - does this method (using Intersect) account for the overlapping buffers? Pretty sure it does (it'd just create two polygons for the same area covered by two different buffers if I remember right), but wanted to check. @Toby - raster should be pretty easy if you have Spatial Analyst. It'd be the Zonal Statistics tool with a bit of math/field calculation. But that would be best asked as a separate question. – Chris W Mar 6 '15 at 2:12
  • Hi @ChrisW I had figure out that the "intersect tool" could solve the problem, there are some wrong with my layer at first, so I couldn't calculate the area size. by the way, I have the spatial analyst tools, could I only use the zonal statistics as table tool to get my results? thank you very much – toby Mar 6 '15 at 3:24
  • @toby It wouldn't be just zonal statistics - similar steps as here are necessary. It's just you'd be able to do it on raster rather than vector data. But again, that's best asked/researched as a separate question. – Chris W Mar 6 '15 at 3:59

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