What is it that you are trying to do in plain language?

For an interface, it's usually best to keep your mouse movement based on your screen's resolution while you World co-ordinates would be displayed using your own values multiplied by your 'zoom level' which would give you your world verses screen display calculation. You can then use this to calculate where your mouse is pointing in your world. This is of course easiest for a 2D world. If you want to know more about 3D worlds, then you'd have to consult someone else here who know more.