The "cluster effect"
According to the Wikipedia:
The cluster effect is the effect of buyers and sellers of a particular good or service congregating in a certain place and hence inducing other buyers and sellers to relocate there as well.
For example in the mid- to late 1990s, several successful computer technology related companies emerged in Silicon Valley in California. This led anyone who wished to create a startup company to do so in Silicon Valley. The surge in the number of Silicon Valley startups led to a number of venture capital firms relocating to or expanding their Valley offices. This in turn encouraged more entrepreneurs to locate their startups there.
Why do I blog this? I was not familiar with this name referring to this concept of emergent/self-organization.