1. A method implemented in a computing apparatus, the method comprising: storing, in the computing apparatus, a plurality of location data points recorded for a time period, wherein each respective location data point of the plurality of location data points identifies: a mobile device, coordinates of a location of the mobile device, and a time at which the mobile device is at the location identified by the coordinates; determining, by the computing apparatus according to the respective location data point, whether the mobile device is within a predetermined region during any of a plurality of time intervals in the time period, by: converting the coordinates of the location into a cell identifier in a grid reference system; determining whether or not the location identified by the coordinates is in the predetermined region based on whether or not the cell identifier is one of identifiers of cells predetermined to be within the region; and determining whether the time at which the mobile device is at the location identified by the coordinates is in any of the plurality of time intervals; generating, by the computing apparatus, a set of visitation data points from the location data points, wherein each respective visitation data point in the set of visitation data points identifies: a respective mobile device, and for each respective time interval of the plurality of time intervals of the time period, whether or not the respective mobile device has at least one first location data point, in the plurality of location data points recorded for the time period, that identifies: a time that is within the respective time interval, and a location that is within the region; providing, by the computing apparatus, at least a portion of the visitation data points as capture history data to a capture-recapture module, wherein: the respective time interval corresponds to a respective capture occasion of a plurality of capture occasions, and whether or not the respective mobile device has at least one first location data point corresponds to whether or not the respective mobile device is captured in the respective capture occasion; executing, by the computing apparatus, the capture-recapture module using the capture history data to obtain an estimate of a population size of mobile devices that are not captured; and determining, by the computing apparatus, a population size of mobile devices that are within the region during the time period based at least in part on the estimate of the population size of mobile devices that are not captured.