We gather data from more than 30.000 weather stations. They fall into one of this category:WMO stations
Professional weather stations run by government agencies. Stations report weather observed in the form of SYNOP codes usually once in an hour, and even less. The latest observation is available sometimes quite late after measurement. The quality of observation is very high. Each station is identified by file number code, for example 11518 is Prague Ruzyne.Airports
Professional weather stations run by airport operators. Airports report observed weather in the form of METAR codes usually once in an hour or less and the observation is available to us immediately. The quality of observation is very high. Big airports report the same weather also in the form of SYNOPs (in other words there are "two stations" at the same place). Each airport is identified by four letter ICAO code, for example LKPR is Prague.Personal Weather Stations
Small weather stations, connected to Internet and run by companies or individuals. They report observation quite often (usually each 5 minutes), but the quality of observation of some of them is low, because the sensors can be placed in wrong location. Most of them do not report wind direction, and if they do, placement of wind sensor is questionable.