Overwatch League Commissioner Nate Nanzer is propposing that the league begin with a slate of sixteen teams. Some of the cities could be based in NA cities: Los Angeles, New York, Boston, Washington DC, Dallas, San Francisco, Seattle, Chicago, Miami, Toronto and Mexico City. Three would reside in the EU: Paris, Frankfurt and London. Two would start in Asia: Seoul and Shanghai. These are, of course, simply examples. The final locations haven't been selected yet.
The information was released by Twitter usr Rod "Slasher" Breslau and appears to have come from a slide entitled "A Global City-Based League Shaping the Future of the Sport".
Blizzard also had this to say:
“The logos and team examples shown at the Leaders Summit were for illustrative purposes only and are not the League's actual teams. That's noted on the bottom of the full slide.” – Blizzard Entertainment spokesperson