A population projection gives a picture of what the future size and structure of the population by sex and age might look like.
It is based on knowledge of the past trends, and, for the future, on assumptions made for three components: fertility, mortality and migration.
Different evolution assumptions are made for each component, constituting different scenarios.
The projections serve as a basis for long-term thinking, particularly in terms of collective development.
They make it possible to analyse population trends if the assumptions are true, but are not forecasts. Individual behaviour, certain public policy actions, scientific progress or unforeseen events (weather events, epidemics) in the coming years may have a lasting effect and significantly influence trends, which the projections do not take into account.
Demographic projections are made by INSEE based on the results of the population census and vital event registers. They can be made for the whole of the territory or for any area composed of several municipalities with a total of over 50,000 inhabitants.
That could be a department, a region, an urban area, major towns or any ad hoc territory.