Existing Projects

When you open an existing project, if any maps were generated, they will be displayed in their respective tabs with a marker that says "PREVIOUS" in the upper left-hand corner. This means that you have made no changes yet. In order to continue working on this map, you will need to reproduce most of the actions you took previously to create the map. The exception to this is the Height Map, Erosion, and any rivers you may have created and saved; the previous height map will be loaded with those features from your project.

So it is normally a good idea to save your Actions (without the height map, erosion, and river components) when you save your project, so you can easily reproduce the map when you need to add more changes.