The words you pick to argue for something are important. They can subtly influence the way people perceive your ideas. So, recently, I've been wondering if it's better to talk about density or compactness.
The recent smart growth literature tends to say "compact" (e.g. "take advantage of compact building design"). On the other hand, Jane Jacobs, whose book, The Death and Life of Great American Cities I adore and was my first real introduction to the concept of a walkable neighborhood uses the term "density" or "concentration" (e.g. "The district must have a sufficiently dense concentration of people, for whatever purpose they may be there. This includes people there because of residence", 200).
Both words are defective in their own ways. I hate that "dense" can also mean "stupid" (certainly not the sense I intend). On the other hand does "compact" really convey the right idea? You can have compact houses, without high population density if the lots are large. Anyway, they're basically synonyms.
They are both suggesting themselves as opposites to "sprawl" or "suburbia". What is the precise dividing line? Hah! That's the million dollar question. I think it's relative to what you're trying to promote. How much proximity to things do you want? How much should people be able to do on foot? How much transit service would you like to support? How much would you like to reduce vehicle miles traveled? How much habitat would you like to save?
How much concentration is a "livable" alternative to the status quo? Yeah, concentration . . .