# Calculating Pop density per sq mi within 1/4 buffer (transit route)?

I have census block data that I have clipped using my 1/4 mile buffer. For each of my census polygons it has kept the original population, is there a way to get the population recalculated just within the buffer?

• What GIS software are you using? What precisely have you tried?
– PolyGeo
Oct 7, 2016 at 16:01
• I have seen this come up a few times and its ugly - think about if you cut a census block to 50% of its area - does that mean you take 50% of the population? Are you comfortable generalizing your analysis to say that population within each block is always evenly distributed? And - what about larger census blocks that have their population outside the area that was clipped? Oct 7, 2016 at 16:04
• The simplest way top avoid uniform distribution is adding address points to the analysis. Compute heads per address using census etc Oct 9, 2016 at 3:42

## 1 Answer

As @DPSSpatial has alluded there is not a simple clean cut solution here. You are bumping up against a couple prominent issues, namely the Modifiable Areal Unit Problem and Spatial Heterogeneity.

Long story short--no matter what you do you'll be introducing new errors into your results. It's unavoidable, and inevitably involves some sort of interpolation.

One of the most simple is binary dasymetric (this is better, in my opinion, than say, areal weighting) areal interpolation.

It was also recommended to me that I take the total population of the block vs the percentage of the block within the buffer and apply the math to the total.

• Your remark at the end of my answer is an example of areal weighting. While that would improve your original method, it's still more error prone that the binary dasymetric interpolation method. Oct 7, 2016 at 18:36