Estimating totals for a smaller polygon from larger polygon attributes

[Chris_Kell]

I'm working with two polygon layers.  The first is a zip code layer whose attributes contains the total number of households in the zip code.  The second layer is smaller study areas.  

I have a memory from course work (possibly false) that their is a tool or tools which will allow me to approximate the number of households within each study area.  For the life of me I can't remember the tool names.  I've done some general searching, but thus far have come up empty.

I'm hoping the community can point me in the right direction.  Thanks for any help you can provide.

Chris Kell

[JoeBorgione · Accepted solution]

You could do a spatial join with both features.  When working with polygon features of populations (houses per zip in your case) you will have to embrace the assumption that the density of houses are evenly distributed across the polygons.

Prior to you spatial join, add a field to your zip polygons and call it OriginalArea, and calculate it equal to the ShapeArea field.

After you perform your spatial join, the zip polygons will be 'smaller' in area.  But you have the original area, so you can divide the new area by the original area and the the ratio between the to.  Multiply the number of housing units by the ratio and you'll get the approximate number of units in your study area.

[Anonymous User]

Hi Chris! Take a look at the tools available in 'Analysis Tools'.

I believe the tool 'Apportion Polygon' will meet your requirements. If this doesnt quite meet your needs, my general trick is to look through the tools in this general area and see what a best fit would be. Sometimes the solution is a couple of tools used in a workflow. Let me know how you go!