The top 25 firms in the Am Law 100 by revenue per lawyer are all based in one of six cities. And New York City lays claim to the largest offices by head count of 19 of these firms.

Big Law is paying a “double premium”—both for office space and elevated employee salaries—as a result of clustering in New York and other high-cost locations like the San Francisco Bay Area and Los Angeles, University of Iowa College of Law professor Gregory Shill notes in a new research paper. Indeed, the newest associate salary scales were set by two New York-founded firms, Milbank and Davis Polk & Wardwell, last week.