# 5.2.2. Estimating internal migration

Internal migration or domestic migration is human migration within a country. Internal migrants are broadly defined as persons who change their place of residence within the country in a given year. The main reasons for internal migration are education, economic improvement, natural disaster, civil disturbance, family, amenity or other socio-economic or political issues. A general trend of movement from rural to urban areas, in a process described as urbanization, has also produced a form of internal migration.

Basic assumptions. The notion of the "usual resident" when analyzing MPD is often associated with the 50%+1 principle. Based on the MPD non-roamers data as a starting point, it is possible to observe the person during 12 months (or more) and consider him/her as the usual resident of the municipality, where more than 50% of communications (incoming/outgoing calls and SMS, internet connections) have been traced in the first half of the 12-month period; the same person can be considered as an internal migrant if the same occurred in the second half of the observation period in another municipality. However, this criterion is not enough for identifying the migrant. Together with the number of connections/communications, it is essential to specify the time also. It can be done in the following manner:

• Based on the IPDR/CDR data, one could distinguish the following categories of the population:
• Night-time population – activities traced from 07:00 p.m. to 06:59 a.m.;
• Day-time population – activities traced from 07:00 a.m. to 06:59 p.m.
• After observing the population during the 12-month period, namely analyzing movements to/from the place of origin (municipality/region), checking the territorial unit border cross patterns, can help to identify the migrant for the specific time point.

Steps and algorithms used for identifying internal migrants for the year X include:

Step 1. Identify the date of the first cross (movement from home municipality to another) of a person in X year (year, day, month);

Step 2. Sum up the number of nights a person spent at home municipality during the 12 months before the first cross, and identify those persons who have cumulated at least 183 days;

Step 3. Sum up the nights a person spent outside the home municipality during the 12 months after the first cross, and identify those persons who have cumulated at least 183 days.

For purposes of the MPD, the usual resident population can be defined in the following manner:

• trace the Night-time Population in X year;
• identify the municipality where the person spent most of his time;
• assume that the person is the usual resident of that municipality (so-called home municipality);
• together with that, it is important to observe the person during the last year and identify the municipality where he has spent at least six (6) months.

Once all the steps for identifying internal migrants are completed, the persons/subscribers can then be classified by statuses as described below:

• the same municipality (the subscriber has not changed the usual place of residence);
• newcomer (the subscriber changed the usual place of residence, i.e. moved from another municipality);