I'm confused by the replies saying that more dense labels would somehow harm usability for driving or navigation. When you're driving, you know where you're going, the map knows where you're going, and it's easy to see the route you need to take. When you're not on a route, denser labels help you to orient yourself with the map and to know when to zoom into a particular location.

That said, I also think the focus on paper maps is misplaced. Old-style road maps had to answer the question, "how do I get there from here?" New-style digital maps don't need to answer that question any more! Questions new-style maps need to answer include:

* I know the name of a place or street; where should I zoom in to see more things around that place or street?

* I need to go to a (gas station / rest stop / hospital); where's the closest one?

* How would I get home from where I am?

* I'm in an unfamiliar place and would like to go "downtown" (where there are restaurants and things to do); where is "downtown"?

* Where is my car right now?

Roads help you to orient yourself with the map, but they aren't as fundamentally important to digital maps as they were to old-style road maps. The visual space of the map might be better spent helping answer questions like these.