I have yet to hear a better definition of economic worth than a buyer and seller agreeing on a price. Clearly, if an employer of 30k people is finding sellers of labor to agree to a lower price in certain areas, then sellers of labor in that area are "worth" that much. Similarly, the employer of 30k people isn't paying people more in certain areas for no reason either. They must have ran out of options for cheaper labor before they decided to pay more.