I've come to think that there's a better way than tiles to draw a map to the screen. I am going to test it for my RTS anyway, so I thought I'd mention it:

We could draw a series of filled rectangles of various colors to the screen that were, say, 5 pixels in width/height, and draw a map, 'Monet' style, as a collection of colored points. It would likely be much faster and use far less memory than importing tiles, and give the game a distinctive look/feel.