Who is "they"? I am assuming you mean openweather. Given that the page linked above details the use of personal weather stations you certainly cannot be referri

Who is "they"? I am assuming you mean openweather. Given that the page linked above details the use of personal weather stations you certainly cannot be referring to WeatherUnderground. Where did you find the source of the data for openweather? Addendum: See my comment below. The number of airports and airfields visible from the air does not get you over 45k.