The wiki page suggests that these are based on social and employment connections that are inferred in part from commute patterns.
Perhaps the pairing of SF and San Mateo reflects growing social and economic links between the Peninsula and SF in a way that eclipses SF and San Mateo's historical affinities with Oakland and San Jose respectively.
http://en.wikipedia.org/wiki/List_of_Metropolitan_Statistica...
The wiki page suggests that these are based on social and employment connections that are inferred in part from commute patterns.
Perhaps the pairing of SF and San Mateo reflects growing social and economic links between the Peninsula and SF in a way that eclipses SF and San Mateo's historical affinities with Oakland and San Jose respectively.