ASPEN, Colo. (Reuters) - San Francisco is the greenest city in North America, followed by Vancouver and New York, according to the latest survey of green-city rankings.

The survey, commissioned by Siemens Corp and conducted by the Economist Intelligence Unit, looked at 31 indicators, ranging from consumption of water and electricity to efficiency standards.

Detroit was the least green of 27 cities ranked, just behind St. Louis, the survey said.

According to the survey, cities with comprehensive plans for sustainable use of resources such as land and energy, did better in the rankings, and that the correlation between wealth and environmental performance was not as strong in North America compared with Europe and Asia.

Siemens has developed green-city indices for Europe, Latin America, and Asia. This was the company's first for North America.

Similar surveys show slightly different results, but with the same broad group of cities tending to flock to the top. For example, the Daily Beast this year ranked New York,Las Vegas, and San Francisco as the top three.

The website factored in criteria including the percentage of residents who admitted in a survey to "no concern or consciousness of environmental issues."

Siemens Chief Executive Eric Spiegel plans to unveil its new index later Thursday at the Aspen Ideas Festival.

(Reporting by Sarah McBride; editing by Carol Bishopric)