A method, system, and apparatus for estimation of a count of mobile devices include receiving one or more probe data points including a location and a session identifier, constructing a trajectory including the one or more probe data points having a same session identifier, constructing a trajectory including the one or more probe data points having a same session identifier and generated by one mobile device of the plurality of the mobile devices, dividing the trajectory area by an area of the observation area, and estimating the count of mobile devices in the observation area from at least the normalized trajectory area. A path of the trajectory is based on the location of the one or more probe data points expanding the path of the trajectory by a radius where a result of the expanding is a trajectory area. A result of the dividing is a first normalized trajectory area.