When I tried to edit the buildings in my area on the map, I basically know some of the attributes of the buildings. But without an aerial photo and addresses, even with the postcode, I am not quite sure about the exact location of the building as the adjacent buildings look quite similar in terms of the shape and form on the map. So what I did was I cross-checked the addresses from Google Map to make sure I put the details into the right buildings.
Perhaps it will be a good idea to include aerial photos or addresses on the base map. Perhaps people can tick whether they want to see them or not. Like now you allow people to switch theme. It will help users to accurately locate the buildings that they are looking for.