New York Times has a nice visualization of how the share of people’s income spent on gas varies across the USA. Their map shows that while gas prices vary across the USA, the amount of people’s income spent of gas varies more. A small part of people’s income is spent in rich urban areas, while gas costs are over 10% in poor rural areas.
Pretty visualization, but I think http://htaindex.cnt.org does a much better job looking at the relationships between transit costs and location.