When it comes to determining electric-car sales, monthly figures published by carmakers are the most readily-available resource.
But they aren't necessarily the sole sources.
Many states don't make vehicle-registration data available to the public, but the ones that do offer an opportunity for more-detailed analysis of electric-car sales in a given area.
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New York state makes its registration data available to the public, and DC Car Geek used that data to determine the most popular electric-car model in the Empire State.
As it turns out, that's the Tesla Model S--by a remarkably wide margin.
There are 1,360 Model S sedans currently registered in New York. That's more than all other electric-car models sold in the state combined.
2011 Tesla Roadster Sport. Photo by Joe Nuxoll.
Add in 39 registered Tesla Roadster sports cars, and the Tesla brand accounts for 51 percent of electric-car sales in New York.
The top three counties for Tesla sales were Westchester, Nassau, and Suffolk--all wealthy suburban areas surrounding New York City.
The next best-selling brand was Nissan, with 535 registrations, followed by Smart with 198.
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Tesla's dominance is particularly remarkable considering the company has only been allowed to sell cars in New York legally since March 28, 2014.
Before striking a deal with state officials and auto-dealer associations, Tesla Motors operated five retail stores despite franchise laws forbidding direct sales.
The agreement allows for Tesla to open additional retail stores in the future.
2015 Tesla Model S 70D, Apr 2015 [photo: David Noland]
Yet it's worth noting that while Tesla owns a very large piece of the New York electric-car sales pie, the pie itself is fairly small.
New York is one of the larger new-car markets in the U.S., but its total of 2,615 registered electric cars is dwarfed by the much smaller market of Washington State.
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There were 12,351 electric cars registered in Washington was of December 31, 2014, according to the state Department of Transportation.
Only about 200,000 new vehicles are sold in Washington per year, but aggressive policies mean it has a much higher percentage of electric cars than New York.
Although the Empire State is among those that have adopted California emissions standards and committed to increasing the number of electric cars on its roads, it hasn't been as aggressive in promoting electric cars as West Coast states.
[hat tips: Lanny via Brian Henderson]