Just five metro areas account for 27 percent of worldwide retail and wholesale colocation revenues, according to researchers at Synergy Research.
The top five metros include New York, London, Washington, Tokyo and Silicon Valley.
The next 10 largest metro markets account for another 25 percent of the worldwide market. So half the world market exists in just 15 cities.
Those top 15 metros include six in the United States, four in the EMEA region and five in Asia. .
Across the 15 largest metros, retail colocation accounted for 76 percent of fourth quarter revenues, while wholesale sales accounted for 24 percent.
Equinix was the market leader by revenue in eight of the top 15 metros and Digital Realty was the leader in two markets.
Other colocation operators that featured heavily in the top 15 metros include NTT, DuPont Fabros, Interxion, China Telecom, 21Vianet, KDDI, @Tokyo, SingTel, Global Switch, CoreSite, CyrusOne and TelecityGroup (since acquired by Equinix).
In 2015 colocation revenue growth in the top 15 metros outstripped growth in the rest of the world by three percentage points, so the worldwide market is slowly being concentrated more in those key metro areas.
Top 15 metros with growth rates of 20 percent or more (measured in local currencies) were Shanghai, Beijing, Hong Kong, Frankfurt, Amsterdam and Singapore. Among the top five metros, Tokyo had the highest growth rate.