Monaco, officially the Principality of Monaco, is a sovereign city-state and microstate on the French Riviera in Western Europe. It is bordered by France to the north, east, west and by the Mediterranean Sea to the south. With an area of 2.1 km2 (0.81 sq mi), it is the second smallest sovereign state in the world, after Vatican City. Its 19,009 inhabitants per square kilometre (49,230/sq mi) make it the most densely-populated sovereign state in the world.

Rhode Island, officially the State of Rhode Island is a state in the New England region of the United States. It is the smallest U.S. state by area and the seventh least populous (1,059,361 as of 2019), but it is also the second most densely populated behind New Jersey. The state has land borders with Connecticut to the west, Massachusetts to the north and east, and the Atlantic Ocean to the south via Rhode Island Sound and Block Island Sound. It also shares a small maritime border with New York.