“Researchers tend to think that informal social interactions—people bumping into one another and swapping ideas—is vital for innovation,” Andrews says. A postdoctoral fellow at the National Bureau of Economic Research, he means that quite literally. An oft-cited research paper on Madison Avenue ad agencies found clear benefits to headquartering close together, but only within a half-mile radius.

What bothered Andrews, though, is that no one knew exactly how and where these vital interactions took place.

Source: How Prohibition Tossed a Wet Blanket on America’s Inventors – Gastro Obscura

Google calls it serendipitous interactions, and apparently it’s been a thing for awhile.