It really is completely up to you. Try it both ways and see which one you feel shows the data better. It is hard to visualize what you mean, because at first I would assume that either way of showing the data would inevitably produce the same end result. Larger percentage of the population would be the same as higher density, and lower percentage would be lower density. Unless you have something more specific in mind, I'd say do whatever makes the most sense with your data.