I did a quick search and didn’t see anything related.
I’d like the ability to get a subset of data by geolocation ie (50 miles from X) or to be able to exclude a certain region.
Good news: GeoIP is now integrated in Piwik, enabling Accurate Visitors Geolocation in your Analytics reports. To enable GeoIP go to the Settings > Geolocation admin page, and follow the short instructions.
You can also get an even more accurate Country & City Database from here to enjoy top accuracy in detecting your visitors locations.
See also the documentation about Geolocation - Analytics Reports in Piwik.