The signals workers send by living in a city
ryanavent.com
ryanavent.com
Since high quality workers congregate there, employers stay despite the cost, to gain the benefit of a high quality workforce.
For example, in a city I need one DBA which costs me $100k. In the country I need two DBAs at $60k each, because if one leaves I'm not confident I can get another of sufficient skill before the business falls apart.
This applies less to larger businesses, which have internal economies of scale and so don't need to rely on the outside market as much. It also doesn't apply to those reliant on lower skilled labor which has a higher supply by default.
Is this even in English?
http://en.wikipedia.org/wiki/Bifurcation_theory
In case you've never studied bifurcation theory.
>Change causes a bifurcation where agglomeration eventually constitutes an equilibrium.
Then add back the extra info.