Liberals claim to have learned one hard lesson from Karl Rove Republicans, and that's the importance of "framing" language. Call the estate tax the "death tax," and suddenly everybody hates the idea. So how do you reframe the notion of density, a word that suggests eating one's spinach and conjures up images of a hated neighbor playing loud music at 3 a.m.? Hint: it involves your feet. The first framing device to make more people embrace the joys of tighter living quarters is carbon footprint, scaring people out of their subdivisions with an ominous rumble of the extinction of the earth if we don't start abandoning our cars and do more walking. The second framing notion is "walkability." A compact, walkable neighborhood sounds sociable, old-fashioned, village-like. Not density, but desirability. And now there's a way to make walkability into a measurable score, so you can compete with your less-dense neighbors almost as readily as announcing your golf handicap. I, for instance, am a 69 (living in Seattle's pretty walkable Madrona neighborhood), achingly close to a 70 which would qualify as "very walkable.". My daughter, who lives in Beacon Hill, a kind of ground zero of Boston pedestrianism, is a 95 ("walker's paradise"). And what are you? Easy to find out. Just go to the newest Seattle online craze, www.walkscore.com. You type in your address, and thanks to a cool GoogleMaps mashup, you instantly know how your address rates according to close-by schools, grocery stores, restaurants, and other businesses. Like www.zillow.com, another Seattle rage that enables you to estimate your house's sale value and (better still) that of your friends and neighbors, you can also put in addresses for others. Bill Gates's mansion, you'll be thrilled to learn, is quite lame on the walk-score. (I'll give you the pleasure of discovering just how bad things are over in the Gold Coast.) President Bush's Crawford, Texas ranch? Big fat zero. This socially redeeming idea came out of the lively brains at Sightline Institute, a Seattle-based Northwest think tank devoted to sustainability and other healthy things. Sightline founder Alan Durning, during his "year of living carlessly," started playing around with computerized ways of analyzing his ''walkshed" in Ballard, and the staff tried for a year to make the emerging GeoWeb tools combine all kinds of listings with GoogleMaps. No such luck, and so the call went out to volunteers and up popped Matt Lerner to work on the project, funded by Mike Mathieu, a Seattle entrepreneur, and assisted by another web developer, Jesse Kocher. A few weeks ago, WalkScore launched, started getting 50,000 hits a day, and viraled away into the nation's brain. Lerner grew up in Topeka, where he was "definitely walkability-deprived. We drove everywhere." He moved from a WalkScore of 51 (anything below 50 is hopeless) to his Seattle house, with an enviable 89. They hope the site will help people make more informed decisions when choosing a place to live, like looking up school scores, crime stats, or even graffiti maps. Lerner says he is not doing this to make money and admits that the service has some bugs. All the listings come from Google, and "a lot of them are out of date or are missing. It's a work in progress, which means the founders are very open about flaws. You can even learn all the bugs by going to their page on what doesn't work. And does walkability work? Sightline cites research showing that residents of compact areas (homes mixed with stores and services, and a street network designed for walking and strolling) are less likely to be obese, suffer fewer chronic illnesses, and may breathe cleaner air than suburbanites by being farther from the "pollution tunnel" of busy highways. Such claims are probably true in a broad sense, but there are interesting complexities in the new science of walkability. All those nifty shops in walkable neighborhoods, for instance, are signs of gentrification, which normally drives density downward by replacing working class families with wealthier singles. Transit stations normally do not help bring more density, since many are surrounded by parking lots or have such high property values that neighborhood services can't pay the rent. Another paradox is that really charming walkable neighborhoods soon line up the pitchforks to oppose increased residential densification in any form. The data is mixed about whether suburbanites are succumbing to obesity, since they are said to have no place to walk. On the one hand is a study showing that New York City, that Mecca for walkers, has added 6.2 years to its average life expectancy since 1990, while the rest of the nation has only added 2.5 years. On the other hand, University of Toronto economist Matthew Turner tracked 6,000 Americans who moved from dense neighborhoods in cities to suburbia. He found no change in weight over six years of his study (maybe not long enough?). People who move to suburbs are normally in search of a strong community life, and cohesive, safe, and walkable neighborhoods. It might be better for the cause to assume that the desire for walkability crosses the urban boundaries and that the inner pedestrian is aching to get out of even the occasional Republican breast, rather than making walkability into another aspect of social snobbery. The truth is, urban culture and values like walkability are extending far into the suburbs and small towns. What the amiably traditionalist notion of walkable community expresses is a kind of blended urban-suburban realm, a soft urbanism. The ideal combines the aesthetic experience of traditional settlement (whether country village or Greenwich Village), without the old inconveniences (dreary stores or teeming tenaments). The ideal is drawn from the fancy neighborhoods of Eurpoean cities of 1775-1900, where people dwell in apartments amid highbrow culture and fine shops. Just look at the sexy ads for Seattle downtown condos and you'll see this gauzy dream. Easier dreamed than accomplished, of course. Cell phones now disrupt the old link of accessibility and centrality that used to favor face-to-face downtowns. As multi-tasking drivers race through red lights and cities spend much less money on creating attractive public spaces where people can sit down and get away from car-clogged streets, we regularly make urban walkability less pleasant. Some cities, such as Portland, really do insist on urban planning that enhances the pedestrian experience. Seattle is so planning-averse that it now seems that only the non-governmental sector (Harbor Steps, Olympic Sculpture Park) can create great pedestrian spaces. The biggest danger, it seems to me, is cost escalation, which drives out the high-character stores and restaurants and bars and replaces them with chains and recognizable-brand establishments. The trick will be to develop a broad enough notion of walkability that it does not become another status symbol, another "score," for the upper middle class.