I thought this was a question about MSA? It seems that nobody got it right, mind you I did check my son's version of MSFS and saw several references here that were evidently taken from that game.
Soooooo,
ICAO Rules of the Air, Annex 2
Procedures for Air Navigation Services, PANS-ATM (Doc 4444)…
Minimum Sector Altitude - The lowest altitude with may be used which will provide a minimum clearance of 300m (1000 feet) above all obstacles located in an area contained within a sector of a circle of 46 kilometres (25 NM) radious centred on a radio aid to navigation.
and, PANS-OPS (Doc 8168)…
Minimum Sector Altitudes or Terminal Arrival Altitudes are established for each aerodrome and provide at least 300 m (1000 feet) obstacle clearance with 46km (25nm) of the navigation aid, initial approach fix or intermediate fix associated with the approach procedure for that aerodrome.
Both can be found in the Jeppesen Airway manual (Revision date 21 Jan 2011), ATC section, pages 107 and 223.