I think that view actually represents about half of the area you highlighted on the map, notice the bridge on the right edge of the screenshot and compare its position to the one on the map.
A valid concern, I agree. The city on the whole might not be as dense as some people might like it to be for realism sake, and we’re not even sure how many of the building are actually explorable in the first place. If I were a betting man, I’d say only around 10% of all buildings are enterable and explorable, and of course a 60-story building won’t have all of its 60 floors freely available to explore.
On the bright side, though, the city looks like it is quite dense but only in certain places, like City Center, Japan Town and some areas in Watson. Plus, ~10% of this city’s buildings is still a lot of content anyway (if it actually were ~10%). And that’s not counting alleyways, sewers, and such.
I’m actually concerned that, with this much explorable area, the writing and art teams might not be able to "catch up" and have enough interesting stories and sights to make many parts of the map worth exploring more than once. But we’ll see when the game releases.