It won't work, since the average number of people living in one building varies with the country. I guess it should be around 10 people per building in USA and 100 people per building in Russia, for example.

I tried to overlay this map with a map showing population density from Google Images and then normalize it with a division filter. I couldn’t find an map with a matching projection however. :(

Check back here in a bit, I'll try to make one. I already have the OSM database and some related glue code, it shouldn't be too far out the way.