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On shopping and the growth of market fairs

So for the last eight months or so, we've been making a conscious effort to buy locally-grown groceries. One easy way to do this is at farmer's markets; anything sold at the New York City Greenmarkets has to be grown by the seller, not bought for resale or on commission or anything like that, so the stuff is pretty much guaranteed to be grown within a two-hour driving radius. There's a huge farmer's market at Union Square several times a week, year-round, with an incredible variety of fruits, vegetables, meat, fish, flowers, etc. and lots of customers... but it takes us 5-10 minutes in the car, twenty minutes on the train, ten minutes on a subway, and five minutes on another subway, plus unpredictable time transferring between those modes of transport, to get there. There's also a farmer's market at Atlas Park, two miles and ten minutes' drive from our home, but it's only open on Saturdays, only May-October, and much smaller, with seldom more than three stalls. Which one do we shop at, how often?


There's a positive-feedback loop: the nearby market doesn't have much variety, so it doesn't draw many customers, so it's hard for the farmers to justify going to it, so it continues to struggle along on three stalls and may well shut down completely. Meanwhile, the Union Square market does the opposite: it has lots of variety, hence lots of customers, hence more farmers are attracted to attend it, etc. I assume this sort of thing has happened throughout human history: if one medieval town managed to get a slightly larger market fair going than its neighbor, buyers and sellers would attract one another to it, enlarging the big fair and shrinking the small one. If the small one continued to exist at all, it would be useful only to those who lived MUCH closer to it than to the larger fair, the definition of "MUCH closer" being determined by the typical consumer's preference curve between short commutes and variety of shopping.

Now suppose the distribution of towns of different sizes follows Zipf's law (originally stated as "the size of the r-th largest town in an area is proportional to r for some positive constant α", or equivalently "the probability of a given town reaching size at least N is proportional to N for some other positive constant τ"). What does this (including the values of α and τ) tell us about consumers' preferences between short shopping trips and variety? If transportation prices rose, or if a religious/cultural movement in favor of simplicity and austerity became widespread, one would expect the preference curve to shift in favor of short commutes, thus favoring the survival of small markets and flattening the size distribution curve (i.e. decreasing the values of α and τ).


Anyway, this particular morning we went to Atlas Park, where there were three stalls and a few customers braving the rain. We got some beets (roots to become brownies or cupcakes, greens to go into Le Menagier's spinach tarts), spinach (for both salad and the aforementioned tarts), fennel (again with the tarts), Honeycrisp apples (before they go out of season), a rutabaga (for Scotch broth, using up the frozen remains of a leg of lamb we had several weeks ago), and I don't remember what else. On the way home, we saw a sign for the new Trader Joe's; we had read a year or more ago that one was coming to Queens, but there had been no news of it actually opening, nor indication of exactly where in Queens it would be. So now there will be a Trader Joe's two miles from our home. Yay!

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