Fact checkers say that cellphone location data is inaccurate. They are deliberately vague about what the margin of error is, though.

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While the average for location data accuracy is 30 meters, there were some significant variations.

The average for Boston is 21 meters; New York 27 meters; Austin, TX, 28 meters; Washington 29 meters, and Chicago 38 meters.

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Sauce: https://www.marketingdive.com/ex/mobilemarketer/cms/news/research/22928.html