Here's a cool map mashup you can play with all Fourth of July weekend long, courtesy of the Center for Neighborhood Technology, via a tip from Eric Hess at Sightline.

Using the Housing & Transportation Affordability Index, you can zoom in on different regions of the U.S. and get an immediate, visceral sense of how much city, suburban, and country dwellers are paying for gas and transportation, both in absolute terms and as a percentage of their total household budgets. Even better, you can compare the figures between 2000, when gas was around $1.81 a gallon, and 2008...

I, of course, went straight to the San Francisco Bay Area, and who would have guessed it? Residents of San Francisco and Berkeley pay a lot less for gas, both absolutely, and as a percentage of their total household budget, than do the suburbs and even further outlying regions. But saying it is one thing -- looking at it is another. Forget all that back-to-the-land utopianism -- the city is where it's at, if you wanna go low-carbon.

But what's really scary is the color-coding changes from 2000 to 2008. In 2000, the urban regions are generally yellow -- indicating expenditures on gasoline between $0 and $1600 per year, and the suburbs are beige -- $1600-$2400. There are only a few scattered orange and red spots -- ranging from $2400 to $3800.

Flash forward to 2008: The entire map is SCREAMING RED, with much smaller patches of orange and minuscule splotches of yellow... in downtown San Francisco and Oakland.