General development plan (PAG)
The general development plan, or PAG (plan d'aménagement général), is each municipality's zoning document: it divides its territory into zones and sets what may be built there.
It distinguishes residential zones, mixed zones, business zones and green zones where building is not allowed. For each zone, it specifies the permitted density, height or use.
Before buying a plot or a house to extend, checking the municipality's PAG avoids nasty surprises: a plot in a green zone will not become buildable just by asking.