Enemy units outside cities visibility needs to be looked at. As of right now it is in the best interest to place your units outside the city as the opponent can not bombard them with aircraft, ships or artillery unless he has a unit very close. Yet this is not the case with cities. I know what units are in the city and how long I need to keep up the artillery. I can easily select the city for bombardment with aircraft,ships and artillery but the 10 units in the stack next to the city mysteriously disappeared.
Perhaps keep units visible, as long as sighted by an aircraft/unit that turn or participated in a battle remain on the map for 1 turn if no units are adjacent to it. If this unit is not spotted or not attacked the next turn then make it disappear.
Another issue is I do not get the comfty feeling when I try and bombard a city with a battleship that the order went through. When I attack with other units the visual indicator is there.