"The first relationships to form in city areas, given any neighborhood stability, are those in street neighborhoods and those among people who do have something else in common and belong to organizations with one another -- churches, P-TA's, businessmen's associations, political clubs, local civic leagues, fund-raising committees for health campaigns or other public causes, sons of such-and-such a village (common clubs among Puerto Ricans today, as they have been with Italians), property owners' associations, block improvement associations, protesters against injustices, and so on, ad infinitum.
"...The crucial stage in he formation of an effective district goes much beyond this, however. An interweaving, but different, set of relationships must grow up; these are working relationships among people, usually leaders, who enlarge their local public life beyond the neighborhoods of streets and specific organizations or institutions and form relationships with people whose roots and backgrounds are in entirely different constituencies, so to speak... [H]op-skip district relationships sometimes originate fortuitously among people from a district who meet in a special-interest neighborhood of the whole city, and then carry over this relationship into their district.
"It takes surprisingly few hop-skip people, relative to a whole population, to weld a district into a real Thing. A hundred or so people do it in a population a thousand times their size. But these people must have time to find each other, time to try expedient cooperation -- as well as time to have rooted themselves, too, in various smaller neighborhoods of place or special interest.
"...A city district requires a small quota of its own Mrs. Roosevelts -- people who know unlikely people, and therefore eliminate the necessity for long chains of communication (which in real life would not occur at all).
"...Once a good, strong network of these hop-skip links does get going in a city district, the net can enlarge relatively swiftly and weave all kinds of resilient new patterns. One sign that it is doing so, sometimes, is the growth of a new kind of organization, more or less district-wide, but impermanent, formed specifically for ad hoc purposes. But to get going, a district network needs these three requisites: a start of some kind; a physical area with which sufficient people can identify as users; and Time."

-- Jane Jacobs, The Death and Life of Great American Cities, 1992 edition, pp 133-136. (bold and typos are mine)