With gas still hovering at $4 a gallon, the Arctic ice caps melting, and our waistlines expanding, walking is more important than ever. But how to figure out whether a particular home or work location is a good one for walking?

Well, there's a way. www.walkscore.com is another one of those wonderful Google Map applications. You give it an address, and it looks at the various businesses in the area and calculates a "walkability score" based on the availability of common services within walking distance.

Needless to say, cities tend to be more walkable than the country, and a number of cities have been trumpeting their "walkability score" numbers since the company released its list of the 40 most walkable cities. Not surprisingly, my old places in San Francisco range from 82 to 91 to 94 to 98, while my Idaho addresses are a dismal 15 and 37. My childhood home, in upstate New York -- where, as I tell my daughter, I had to walk to school uphill both ways in summer heat through snow up to here -- scored 57.

Noting that the "number of nearby amenities is the leading predictor of whether people walk," the Walk Score algorithm awards points based on the distance to the closest amenity in each category, the website explains. "If the closest amenity in a category is within .25 miles (or .4 km), we assign the maximum number of points. The number of points declines as the distance approaches 1 mile (or 1.6 km). —no points are awarded for amenities further than 1 mile."

The website and algorithm are constantly tweaked, by people adding missing amenities or missing categories. And the website is the first to admit that its algorithm has its faults -- it doesn't take into account factors such as public transit, block length, safety, hills (or San Francisco might not have done so well), and weather (which is a big factor in Idaho, where I describe spring as "the week between 'too cold to be outside' and 'too hot to be outside'").

And it uses "as the crow flies" directions, not routes following roads or paths. "This means if you live across the lake from a destination, we are assuming you will swim," the website explains. "And if you live in a subdivision with long curving streets with few intersections, we hope your neighbors don't mind you walking through their back yard" -- a significant factor when such subdivision design can double the distance needed to travel. The company is looking at adding support for the relatively new Google Walking Directions in the future.

Moreover, the company is promoting the use of walkability scores by cities for urban planning and in real estate ads to attract people. In a world where "green" factors are becoming more important, www.walkscore.com provides a useful function.