Well, I didn't answer this message the other day, because I'm not entirely sure about the answer. I don't know where everyone has been lately, but in any case, I'll give it a try.
Even though coordinates are given in Inkscape, they aren't like...nailed down. Because it's vector-based, not raster (raster means a point on an image corresponds to a pixel on the monitor -- I think). So Inkscape's coordinates do not correspond to the pixels, they're more of just like guides. That's about the best way I can explain it, but you could get a much better explanation (right away) from Wiki. And hopefully more knowledgeable members will answer sooner or later
Anyway, you could draw the map using coordinates. Whenever the Selection Tool

is active, you can see dimensions and coordinate settings on the right side of the toolbar. And when the Node Tool

is active, you can also see coordinate settings for the nodes on the right side of the toolbar.
I'm not familiar with your mapping work, so I can't say whether Inkscape does exactly what you want. But I do know that you can use coordinates in most situations.