(this is not for the "internal" gui or a touchscreen device gui)
the + and - magnifying glass buttons for zoom in/out, on the toolbar, are currently a bit inefficient because they don't provide the user with a sense of scale at all. I would suggest either finding a way to use a gtk scale, or, more simply, to use a gtk combobox. It could have values that indicate the zoom level. For example:
Values in percent, whereas 100% = 1:1 scaling (unlikely to happen, but still). So the values would be something like
5%
10%
15%
20%
25%
30%
35%
40%
Another way to put it is to use absolute units (km, meters...), but I am not sure this would be clearer/better, or that it would be feasible at all.
