requirements for making a minimap?

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I have scoured the forums for a while now in regards to making a minimap. The o lyrics information I can find is that you can use the offline editor and press "m" to make a big map and then resize it to be a minimap. And that there are other programs you can use to make higher quality images. My questions, however, are the following. What are the sizes the image needs to be to properly be displayed? And how do you set the minimap? I did not see documentation on the graal bible in regards to the minimap, only big map and gmap.