DC in the US is a solid counter example as low density city older than the car. Density is based on a huge range of factors with for example geography playing a significant role. Another huge factor is they type of industry. Garment factory's for example have historically had very high density's where Iron Works are much lower density.
DC is a pretty good counter example. As you say the type of work matters, and DC has never an industrial town. It was also a planned city. It was intended to not be dense from the start. Something like 40% of DC is federal government land.
DC also is doing a decent job at using mass transit to re-densify areas. The orange line corridor is making suburbs become dense. That is pretty unique in America.
For a city that was "intended to not be dense from the start", it sure is up there as far as density and would be #16 on the list if it counted as a part of a state.
DC is incredibly dense by American standards and is actually one of the very few places in the US that you can get by without a car (which is, of course, priced into exorbitant rents and property prices)
I guess what I meant to say is that the grandparent comment is blatantly false. DC _is_ a high density city and is much more like a European city in that it combines decent public transport and medium-rise developments.
