Each call activity in the positioning database for the current
study includes: (a) the time of the call event; (b) the randomly
generated ID number for every visit made; (c) the randomly
generated ID number of every phone used as the ID of one person;
(d) the country code of the phone (the country where the mobile
phone is registered is seen as the country of origin and determines
the nationality of the visitor); and (e) x and y coordinates of the
antenna. The trip duration and the number of days spent in
different counties or local municipalities can be calculated based on
the available data. An example of an original log statement of the
database is shown in Table 1.