O4W stands for Old Fourth Ward. The northern part of that neighborhood, according to the present boundaries, is centered around Historic Fourth Ward Park, which is where there was a spring, and now there’s a pond that’s designed to impound stormwater. Here’s a bridge to nowhere, or a pier, over that water.
All the buildings on the right, and most of those at the far end, have been built since the park, and the BeltLine trail you can’t see (to the right behind the buildings), were established less than a generation ago. The star-shaped pattern is from the aerator fountain, which stopped just as I snapped this (just the way I timed it haha).