Sounds like if you have a record of a lot of location/timestamp data for people, you look at the distance difference divided by the time difference. Now you have average speed for any pair of points. Now filter where the average speed is as fast as a Boeing jet. That filters out most of the data except for people who are almost certainly on a plane. Et voila, you now look at those data points geolocation and you have people who traveled from one city to another because you already have the location. Compare City1 -> City2 with any public flights in those cities around those times and you know who flew on what flight from where to where and at what time.