Extendable Map Format

Creating a Map is a very time consuming process even so creating a tileset. Both pieces of hard work should be able to survive all changes in program flow and game philosophy so that work once done must not be redone. Nobody knows what happend in a long process of game development.

What is needed for an extendable map format or the other way round: What can change in games life? To be prepared for the future the map format should show following qualities:

There might be some more. The complete this list is the better is the resulting map format.