# How to calculate which US counties border the ocean?

I have a shapefile with boundaries of US counties. I want to figure out one seemingly simple thing - which counties are on the Atlantic ocean? NOAA maintains a list of coastal counties, but this includes counties that are on the "coastal watershed", which is not quite the same thing (I'm basically trying to identify counties with a coastal view). The same problem comes up when I try to use a NOAA GIS file with coastal boundaries.

It seems like the simplest way to do this would be to calculate whether a county has any border that is not shared with another county. Then I could throw out states that don't border the ocean (to eliminate the Great Lakes) and manually eliminate Texas counties that border Mexico. But I can't figure out how to do this calculation.

• Maybe load up an oceans layer and find counties that share a border with that layer? Or do a slight buffer on the ocean layer and find intersecting features. There are numerous ways. – Branco Aug 11 '15 at 15:19
• if you don't have another GIS layer with the Atlantic Ocean, the fastest way is to directly select manually (takes a couple of minutes). For automated solution, please specify your software/licence level. – radouxju Aug 11 '15 at 15:25
• Might be one of those situations where looking at it and doing it manually is a whole lot quicker and less hassle. – pvdev Aug 11 '15 at 15:36
• I'm worried that the ocean layer will also include these "watersheds" or won't line up perfectly with the US counties map. I have ArcGIS 10.3 with pretty much all the add-ons. – user2472081 Aug 11 '15 at 15:38
• @radouxju - don't forget the Pacific and Arctic oceans as well as the Atlantic - they also border the USA! Though, selecting states by hand is indeed simple enough. Alternatively, make the oceans! If you have Canada and Mexico to avoid false positives, then make a huge polygon to contain them, difference it with the land = sea. Then test for an intersect or touches. – MappaGnosis Aug 11 '15 at 15:51