The FSX Map view is not intended to replace VFR and Low/High Altitude Route charts.
FS does have a world grid system with a MSA (Minimum Safe Altitude) for each grid.
When you create a flightplan, FS will set the altitude for the highest MSA for the grids the flight plan crosses. FS is not setup/ programmed to varying altitudes on different segments of a flight plan, rather one altitude in the FP.
You have the option of varying your altitude by requesting different altitudes, but you have to do the research from external real world sources.
@ PawPaw's house - near KADS, Addison, Texas, USA