[Sandy]

...town of 30 000 inhabitants...
The youths are said to be residents of Saint-Dizier's low-income housing project, Vert-bois, which is home to 12 000 people.

Nearly half the people in this town live in one housing project? WTF?

[Gritty]

Nearly half the people in this town live in one housing project? WTF?

Here's a map of the city, with the "off limits to non-Muslims" area marked in red. You're right. It is about one third of the town.

Saint Dizier - Vert Bois

This comes from a French publication which shows the hundreds of ATLAS DES ZONES URBAINES SENSIBLES "off limits" areas in France, which native non-Muslim Frenchmen are warned to avoid for their own safety.