OpenStreetMap
In a completely unscientific calculation, if you take the total kilometres of ways at the end of this page and divide it by the estimated kilometres of roadways at the CIA Factbook, you find out that we are 69.28% complete worldwide, at least as far as roadways go!
Discussion
Comment from Gary68 on 11 August 2008 at 13:22
but ways here are also rivers, pathes, tracks and even the perimeters of things...
Comment from David Dean on 11 August 2008 at 13:53
Well, I did say 'completely unscientific' :) However, if you add up from highway=residential down to highway=trunk in the same table you get 18257352 km, which makes the completeness figure 56.45%. Still not too bad.
Comment from David Dean on 11 August 2008 at 13:55
And, I'd reckon other than maybe coastlines, the other ways like rivers, footpaths, cycleways and area boundaries are probably a fairly small amount of kilometreage compare to the car-navigable roadways in OSM.
Comment from David Dean on 11 August 2008 at 13:58
Oh, and if you look here you can see that the CIA figures include unpaved roads in that total, so tracks should be included.