Summary: Island cities invulnerable to assault due to pathing

Description: When the PC sets an Outpost/City on an Island (for instance a 1x3 island), they are unable to be attacked due to units in the water unable to get on the land to start the attack.  This is especially frustrating when it is an enemy with an Oil resource they aren't using, due to how scarce oil is in the game.  

Steps to reproduce: Let another culture develop territory on a small island at sea.

Reproducibility: 5/5 (every game AI has taken over a small island or expands farms/etc to all the edges of an island)

My other thought is why is Oil not able to be extracted on the terrain like it is in real life (as well as in the ocean)?  I have yet to see Oil anywhere except off the coast.