There are many ways to link classic-era United States ("US") commemorative coins by geography. Here's a set of four issues that are connected by a body of water - the Long Island Sound.
The Long Island Sound is a body of water that forms a tidal estuary (a body of water that contains salt and fresh water). It stretches from New York City in the west to Westchester County, CT in the east - a span of approximately 110 miles; it covers approximately 1,300 square miles. (Note: The Sound borders most, but not all, of Connecticut's shoreline; it does not extend to Rhode Island.)
Map of Long Island Sound
(Image Credit: Long Island Sound Partnership. Fair Use, education.)First up, the 1935 Connecticut Tercentenary Half Dollar:

Staying in Connecticut, the 1936 Bridgeport, CT Centennial Half Dollar:

Moving west to just north of Manhattan and the Bronx, the New Rochelle, NY 250th Anniversary Half Dollar :

And finally, Long Island itself via the 1936 Long Island Tercentenary Half Dollar:

For other of my posts about commemorative coins and medals, including more about each of the coins referenced here, see:
Commems Collection