about maping system

when i go threw it with tab im wander why some of the map vanuishs when i go back does it keep randomly generating the map?

Areas are instanced and generally generated randomly (although they follow the same general layout).

If you leave an area, after some time (it used to be 15 minutes, but it was reduced to 8 minutes, I'm not sure whether it's 8 / 15 / something else currently) it will reset and then get generated again when you re-enter the area.

If you stay in an area, it shouldn't change.