More can always be said, but /u/restricted_data has addressed the discussion of targeting an uninhabited island, or isolated military installation here and here, as well in his linked blog posts, which I highly recommend.

To summarise, there was some consideration given to the idea of a "demonstration" bombing, of utilising the atomic bomb against an island in Tokyo Bay in order to show off the power of the new weapon, or against the IJN's anchorage at Truk Lagoon. However, the atomic bombs were incredibly rare at the time, and the military viewed such a use as effectively wasting an incredibly valuable asset. The psychological impact from the destruction of a city was a major targeting consideration, and anything less would've been "wasting" the impact of the bomb.