To begin, let’s be clear about one thing:  we’re huge fans of Walk Score–the free Internet based service that rates every residential address in the United States (and a growing list of other countries) of a scale of 0 to 100, based on their proximity to a series of common destinations.  The concept and implementation of Walk Score are brilliant, transparent, and well-documented: not only can you see the score for your house or any other, Walk Score shows you which destinations were used in calculating that score.  And did we mention, it’s free.

The power of Walk Score is its market-moving value:  Americans are increasingly looking to live in vibrant, walkable communities, and Walk Score gives home buyers (and now apartment renters) a clear and simple tool for assessing the relative merits of different locations. (Which is undoubtedly why it was acquired by real estate website last year).  While there’s a lot more to walkability than just proximity to destinations–urban design, the quality of the built environment and pedestrian infrastructure matter too–Walk Score has substantially advanced the conversation about how to measure and make walkable places.  To their credit, the team at Walk Score has responded to criticism and continued to refine and extend their product, incorporating a Street Smart algorithm to track the street grid rather than relying on straight line distances, and adding measures for transit and bike access.  All this is exciting and useful: We think that giving consumers better information about their choices is pretty much an unalloyed public good.

And–full disclosure–in 2009 we got the cooperation of the team at Walk Score to provide data for a research project looking at the connection between walkability and real estate values.  Our research–done independently from Walk Score–showed that in 14 of 15 cities that we examined, walkability was positively correlated with home values, even after controlling for a host of other observable factors (like neighborhood income, numbers of bedrooms and bathrooms, home size, distance to jobs) that we know influence home values.  You can read the study “Walking the Walk” here.

Yesterday, Walk Score released its latest analysis rating the of walkability of major US cities.  Scores are produced by averaging the walk scores for different parts of the city, weighted by the population.  According to Walk Score, New York is the most walkable large city in the U.S., with an average walk score of 87.6, followed by San Francisco (83.9) and Boston (79.5).  The complete rankings are here.

Because they’ve been gathering data for a number of years, Walk Score is now in a position to report the change in walkability at the city level.  This should be a key indicator for mayors, planners and citizens.  Becoming more walkable is likely to be a proxy for an improving local economy, and suggests a city is becoming more accessible to its residents.  Walk Score reports that several cities have notably better walkability than a few years ago year ago:  Miami’s city-wide Walk Score increased by  more than 3 points, Detroit saw an increase of 2.2 points, and New Orleans recorded an increase of 0.7 points.  These particular results are a bit muddled by some changes to the Walk Score algorithm since 2011, but going forward, this promises to be an important tool for tracking progress at the city and neighborhood level.  Kudos to Redfin and Walk Score for making this information available.

But enamored as we are of Walk Score, we’re compelled to point out one glaring flaw in their rankings: the use of municipal geographies to compute scores for ranking purposes.  Their methodology looks at the average level of walkability only for addresses located within the city limits of each city.  Because municipal boundaries are so varied from place to place, municipalities are a poor unit for comparison, particularly for this kind of spatial data.  Using municipal boundaries for comparative work inevitably ends up comparing apples to acorns, and produces rankings that are at best misleading, and at worst, arguably wrong.

Chicago and Miami provide a case in point.  According to the Walk Score ranking, Miami is more walkable than Chicago–Miami’s city-wide walk score is 75.6, edging out Chicago’s 74.8–a finding that immediately struck our colleagues who have lived in the two cities as counter-intuitive, to put it mildly.  But the problem isn’t a flaw in Walk Score, it’s that these two municipalities represent wildly different chunks of their respective metropolitan areas.  The City of Miami encompasses only a small portion of the Miami-Ft. Lauderdale metropolitan area (the densest parts of downtown Miami and close-in urban neighborhoods); Chicago covers a much larger swath. The City of Miami is just the most densely housed 400,000 people in South Florida; while the City of Chicago is 2.7 million people.  There’s little doubt if we measured the walkability of the Chicago neighborhoods that were home to that region’s 400,000 or so most densely housed residents, we’d find a much higher Walk Score.

It turns out that metropolitan areas are a much more sensible basis for making comparisons and presenting rankings.  While municipal units may be a valid geography for some comparisons (related say, to elections or public finance) they can easily be misleading or wrong for making comparisons that involve economics and geography.  Look for a future CityCommentary digging deeper into this problem–and outlining how to avoid it.

In the mean time, here’s an unsolicited suggestion for the team at Walk Score:  can you use your database to create a count of the number of persons living in homes and apartments with a Walk Score of 80 or higher “very walkable” and “walkers paradise” in each metro area?  This would be a much more compelling indicator of how metro’s stacked up as walkable places than a single average score for a city–or a metro.

So, in the end, its one step forward (another year’s worth of data and the promise of tracking changes in walkability over time) and one step back (using municipal boundaries for comparisons).  This last glitch is easily fixed–and knowing the team at Walk Score, it certainly will be. In the mean time, their excellent and informative Walk Score data for individual properties is performing a vital public service and helping move markets.