It is almost a truism to say that a self-supporting community must somehow produce and export goods and services equal in value to those that it imports and consumes. There are exceptions, of course, but they only serve to prove the rule: A college town that depends on student tuition and the income generated by college endowments. Or a retirement community whose economy is underwritten by the pension benefits and life savings of its members. It is also possible for a community’s members to work elsewhere, but in those cases the community is not truly self-supporting in the sense we are using the term.
That being said, what is the smallest collection of neighborhoods which might reasonably expect to be self-supporting over the long-haul? We know it would be unwise to depend on the output of a single factory alone if only because factories sometimes downsize, move away, or go out of business. Thus to be safe there would need to be a certain number of factories, no one of which was so big -- employed so many people -- that the community could not survive without it.
With these facts in mind let us try to imagine a small country town of, say, between 15,000 and 25,000 inhabitants. That would be equivalent to a hundred neighborhoods or so, each neighborhood composed of several dozen families living on one-acre homesteads. What would be the best (most convenient, most economical) way to lay out the neighborhoods? How should they be arranged in relation to the factories and to the places where we would shop, the local courthouse, public schools, and the like?
Here is a rough sketch of the answer to this very general problem as originally worked out in England over a hundred years ago. It was known as the garden city concept and it was this idea that inspired the English town-planning movement: