My analysis of the projection function, roadmap_math_compute_scale in roadmap_math.c, suggests Roadmap does a WGS84 projection of some sort. I really haven't dwelved into the math any futher to say if it is doing cartographic projection or not.. although the comments suggests it does- he says the projection tries to compensate for curves around the poles. I'll trace the code more and see what it's doing and let you know if I figure anything else out.