How to estimate population within a polygon

06-07-2016 01:35 PM
New Contributor

All – I am in need of some assistance –

I have a polygon area – Dam Inundation Area (Blue)


A polygon area of Census Block which includes population (Orange)

I need to get a population estimate within the dam inundation area

I am thinking that I will need to distribute the population somehow and then possibly an intersect??

Has anyone needed to do anything like this and can send some steps.  I do have spatial analyst extension if needed.



Inudation Area Question.JPG

0 Kudos
1 Reply
MVP Esteemed Contributor

You'll have to settle for a little bit of error for this:  In your population data, add a filed called OriginalArea as a double, and calc it to equal the shape area field.  Then clip/intersect/identity, whatever your population polygons with your inundation polygons.  Add a a field called Percentage in the resulting feature class.  Calc it to equal (new) ShapeArea / OriginalArea.  Then calc your population field to equal Percentage * Population.

The error in this comes from the fact that population isn't evenly distributed across a census block, block group or track, and the calculation makes that assumption.  But when it comes to dam inundation studies, it's close enough.  At least it was when I was doing them for State Engineer's office here in Utah some years back....