For decades, a tried and true measure that planners have used is the 5-minute walk. Sometimes we use the wonky version, "pedestrian shed" or still wonkier "per shed." The basic idea being: a successful walkable neighborhood will have nearly all of life's necessities within a 5-minute walk, which equates to a 1/4-mile radius.
We often trot out Clarence Perry's diagram from 1929 as an illustration of the idea:
The 5-minute walk is admittedly a simplistic measure, but there is some truth to the notion that it corresponds to the distance the majority of people will willingly walk for goods, services or entertainment. Once that walk starts to reach ten minutes, studies have shown that fewer people will choose to walk. As a sidebar I'd suggest that this has a great deal more to do with the quality of the walk and the neighborhoods, and less about the actual distance. I've written in some detail here about my personal experience in Savannah in this regard.
Charles Wolfe & J. Alexander Maxwell have been exploring this idea from a slightly different angle with their "400 meter rule," which essentially is 1/4 mile of length. They've been studying hundreds of cities built before the car became ubiquitous in order to uncover any commonalities of measurement. That 400 meter distance holds pretty consistently as a good measure of human-powered movement.
This week, Walk Score added even more data to the mix when they released an analysis that mapped accessibility to fresh food from neighborhoods in cities all over the country. The results are predictably pretty grim. Only a handful of cities rank over 50% of locations where people have that kinds of access and the majority are well below that mark.
Sarah Goodyear summarized:
So the Walk Score ranking is a blunt instrument. But what it shows, in its blunt way, is a remarkable gulf in the way American cities are constructed. In the list of 50 cities (which I obtained in spreadsheet form from Walk Score), only New York, San Francisco, and Philadelphia have more than 50 percent of residents within the magic five-minute walk to the store. Oakland and Miami, both with 49 percent, round out the top five, with Boston (45) close behind, and Washington D.C., Chicago, Baltimore, and Long Beach all at 41 percent.
Then things rapidly go downhill. After you pass Seattle, ranked 13th with just 31 percent access, no other city in the U.S. cracks 30 percent, and the bottom 22 cities of the U.S. top 50 by population all have 10 percent or fewer residents within a five-minute walk to the store.
The numbers paint a picture of a dramatically divided nation, one in which even residents of the nation’s largest cities rarely have quick access via active transportation to the ingredients for fresh and healthy meals.
Below is the ChoiceMap for Savannah, which clocked in at only 14%. It's not easy to read at this scale, but you can tell that basically all of the historic districts north of Victory Drive meet the 5-minute rule, but the vast geography of the city beyond that area largely does not.