Mark location tool
At the moment, you place your cursor, right click and select mark location. It would be much easier and more precise, if there would be a tool for marking locations. E.g. you would select the tool from the toolbar, then click on the map, and the location would be marked.
Multiple marked locations
There's no possibility to have multiple marked locations. That should be added. They could show in a list in the tool window
Marking location from tool window
Also if you like to add more locations, it could be handy, if you could add locations from the tool window. There could be same mark location mouse tool.