On the French IGN 1:500,000 charts there are places marked with a red square/dot which aren't supposed to be flown over below, according to the map legend,1000 ft AGL. On the equivalent Belgian 1:500,000 chart these areas are shown as "P" (prohibited) areas with a circle of a few NM radius with a  more restrictive height requirement, typically 3300 ft, in the few examples I have found.

One example of a site with special marking is called "Pitgam" approx. 10 NM south of Dunkerque.

These places areas aren't shown at all on SD maps as far as I can ascertain. Is this because their positions aren't promulgated via usual aviation channels?

Tony Nowak