If we all lived in an urban density that equaled that of Brooklyn (something many people would consider perfectly livable) the entire population of the US would fit into the state of New Hampshire, approximately 9,000 square miles. Wait... what?
Yes, 300 million people would fit in the fifth smallest state, with room left over for a lot of parks. If we tweaked the shape of this 9,000 square miles into an actual square shape, it would measure about 95 miles on a side.
Yes, 95 miles.
So the farthest we'd live from anyone would be 95 miles. A two hour drive, maybe three in rush hour traffic. You could bike anywhere, walk anywhere, take the subway or the bus anywhere. What would this world be like? Would people actually know their neighbors names? Would we walk to work, and take a stroll in the evening? Would we take pride in our homes, and our parks? Make an effort to keep our streets clean?
Expecting people to be willing to make such drastic changes may be too optimistic, but it demonstrates how little space we really need to live. A radical idea, but one that can inspire change.