The study of population trends is based on the calculation of a certain number of standard indicators which make it possible, in particular, to apprehend the probabilities of the occurrence of demographic events (birth, death, marriage) and the average ages of occurrence of these events: fertility rate, marriage rate, average age at marriage, life expectancy, etc.
Demographic indicators are calculated from vital statistics and population estimates. The geographical scope covered by these sources covers the entire French territory, metropolitan France and overseas departments, since the dissemination of data for 1998.
Previously, the statistics published by INSEE concerned metropolitan France alone. However, some indicators have been partly backcast. These sources have also seen their geographical scope evolve over time in line with changing borders and have experienced specific problems of exhaustiveness, particularly during the two world wars.
For historical series prior to 1946, the geographical scope varied according to changes in the boundaries of the national territory. Between 1901, when the series published by INSEE began, and 1946, it only corresponded to the current boundaries from 1920 to 1938.
Until 1919, Alsace (Bas-Rhin and Haut-Rhin) and Moselle, annexed by Germany, were not part of the national territory. These three departments became French again when the Treaty of Versailles was signed on 28 June 1919. On that date, they brought 1.7 million inhabitants to France. During the Second World War, Alsace and Moselle were again excluded from French territory.
On 1 January 1944, Corsica was also excluded from the population estimate because of the absence of statistics. Its data are available again on 1 January 1945.
From 1946, the territory of metropolitan France is within its current borders, with the reintegration of Alsace and Moselle, and the integration of two previously Italian communes (Tende and La Brigue, 4 126 inhabitants at that date).
In 2007, two islands, Saint Martin and Saint Barthélémy, previously administratively attached to the department of Guadeloupe, became independent. They are no longer part of the France field.
In March 2011, the Mayotte overseas collectivity became the 101st French department. It will gradually be integrated into the France field.
Backward projections were carried out to obtain indicators within the current boundaries.