Place of publication is required for books, not periodicals.
The place of publication is the "name of the city where the publisher is located." The place can be found on the title page or verso of the title page. It is not necessary to identify the state, province, or country after the city name (5.5.2).
London: Oxford UP,
When more than one city is listed for the same publisher, use only the first city.
If no place of publication is indicated, use the abbreviation n.p. (no place).
N.p.: U of Gotham P, 2008.