G.T.A.2 Map Editor

[hwnd]

User137 or anybody.

I have a third party OpenGL app, actually GTA1 map editor from 1998, maybe uses OpenGL 1.1 or something, dunno. What's interesting in it is that it creates very nice minimap from map. I see that minimap uses same colors as actual map and any changes made in actual map are immediately visible on minimap.
Its a C++ MFC app, there is no source available.

Also it has option to also draw or not to draw transparent tiles on minimap.
This makes me think that it actually draws scaled down tiles, but how he does it so fast.
Thats the key question.

Any ideas how it creates that minimap? It seems that it draws actual map in small size somehow, like scaled down someway. But all minimap colors are same as in actual map and i would like to do the same in my editor.

In opengl, what could be used to create such minimaps? I dont think that it draws whole city twice, one in actual size and one like scaled down version. Or does it?
And its fast, changes in big map are immediately modified on minimap also.

I once tried drawing all tiles in 1x1 pixel for minimap but something was very slow. But it gave me same colors like in actual map.

EDIT: ok i remember, drawing 1x1 pixel tiles for 256x256 minimap was slow.

But one idea i have atm is to have big global list where all the current (LID) tiles are, actually their ID numbers and only these that are currently used will be scaled down to 1x1 and drawn with StretchDraw and not all.

I just need something fast.