Shipwreck

The site of the shipwreck of the Annie C. Maguire is commemorated with this painted white message, on the site of the wreck:

This post's theme word is pelagic, "of or relating to the open sea, as distinguished from the shallows near the coast." The lack of visual references makes pelagic navigation more difficult, but assuages most fears of collisions.

There goes Manhattan

Identifiable from the sky. A very distinctive appearance; just like maps.

This post's theme word is foursquare, "firm, unyielding; frank, forthright; square in shape." The foursquare city planning made navigation easy.