Combining polygons

[TarineeK]

I have three drive-time analysis boundaries/polygons created and they all overlap significantly. I need to be able to merge them into one single one so that I can determine the collective population captured in these catchments together. I then need to see how much this overlaps with a fourth drive-time catchment.  

When I merge the layers and run a "summarise within" analysis to determine the population for the first three together, I keep ending up with three quoted populations as though the polygons are still seperate. When I run a dissolve function, I get lots of quoted populations rather than 1 collective population, so I am unable to latter map this over the 4th catchment to determine the overlap. 

I use arcGIS pro and arcGIS Online and have had no luck after days and days of trying. 

Thank you! 

[DavidPike]

I'd say something went wrong with your merge, or that you're using the wrong input to summarize.

use the Dissolve tool and ensure that one single feature is returned by checking the attribute table, then perform the summarize.

[JoshuaBixby · Accepted solution]

I think what you want to do is Union the first three polygons into a new polygon.  Merging three layers/data sets with a single polygon into a new data set simply creates a new data set with 3 polygons.  If you want a singular polygon, you need to union them into a new polygon.

[TarineeK]

this worked perfectly! thank you!