Find the Proportion Of A Polygon From an Overlaid Buffer

[GarrettRSmith]

Hello

I am working on a project where I am running a 1-mile buffer from a point. The buffer is then overlaid on census tract data. I was wondering if there is a way to find out what proportion of a census tract is contained with the buffer?

I am trying to come up with a way to calculate the population of that census tract that is not fully contained within the buffer. For example, if a tract has 100 people and that tract is only crossed by 10 percent of the buffer, I would want the population to be 10 and not 100. 

It is in an urban area so there are a number of tracts that are like this within the various buffers.

Thanks

[DanPatterson]

Tabulate Intersection (Analysis)—ArcGIS Pro | Documentation comes to mind.  Or have a look at the other overlay tools in the An overview of the Overlay toolset—ArcGIS Pro | Documentation for other options

[GarrettRSmith]

Hi Dan.

Thanks for the suggestions. Tabulate intersection gives the percentage of the polygons that make up the buffer and none of the other Overlay tools are what I am looking for.

I am including a picture of the project so you can see what I am talking about.

I have a study site (red point) and a one mile buffer overlaid on census tracts. As you can see, some of the tracts are fully contained within the buffer so I can assume that 100% of a value, say total population, would be appropriate for the analysis. The tracts on the outer edges of the buffer however are not 100% within the buffer so I cannot assume that 100% of a value, population again, would be appropriate for the analysis.

I am most interested in finding out what percentage of the outlying tracts fall within the buffer. I can do the calculations outside of Arc if that is needed. I would imagine with the strange nature of census data and other administrative boundaries that someone would have come up with a way to so this. 

[DanPatterson]

If you have the total area and the areas from tabulate intersection, then you can use a simple field calculator expression to get the percentage

[GarrettRSmith · Accepted solution]

Hello

I found a way to do it all through Fields.

1. Create and calculate an area field for the unclipped census tracts
2. Clip the census tracts to the one-mile buffer 
3. Create and calculate an area field for the clipped census tracts
4. Create a percentage field dividing Step 1 from Step 3
5. Create a Clip field for each count demographic and multiply the unclipped demographic value by the percentage

This is by no means elegant but it works.

Thanks for all your help.