One obvious thing that is missing from our general user interface is that we have no way to save or load a user session. That is, saving the current state of loaded layers and their properties, the sequence of layers, general map options, projection, zoom level, and so on, so that we can return to the same application session we previously used. The Home tab will be a good place for a load and save session button, which can also be called on with the keyboard shortcuts Ctrl + O and Ctrl + S.

In order to save these settings, we will have to come up with a file format specification as well as an identifiable filename extension. This can be, for instance, a simple JSON text file ending with .pgs (short...