Paul -- it's actually more complicated than that. A role playing grid can have a lot of land area for big campaigns, while still being a tight-knit social grid. And some education grids fit a lot of activity into a small land area, cycling multiple classes through the same setups.
Then there are grids that are nothing more than a couple of regions that draw a lot of traffic -- a freebie mall, say, or a hyperport. Or a museum or music venue.
Finally, say a grid adds a huge nature park, just for the hell of it. The nature of the grid doesn't change, but all that empty parkland, while pretty, will lower the density count. Same goes for open seas for sailing.
There's no one-siZe-fits-all formula. Each grid is unique and beautiful in its own way.