Each world will generate maps of a level equivalent to the world number - maps created while on world 9, will be lvl 9.
There are currently only a set number of item unlocks per level. So once you've collected all the level 9 items, there will be no more until you create a map on world 10 (a level 10 map). However, it may be worthwhile to sit on a map and grind out resources for a bit so that you are better prepared (better gear / more gyms / more trainers) for the next level.
Last I've checked, starting at lvl 6 (I lost track where in here the Mansion unlocks):
- Map lvl 6
- Shield, Dagger, Boots (mk II)
- Map lvl 7
- Map lvl 8
- Map lvl 9
- Battleaxe, Shoulderguards (mk II)
- Map lvl 10
- Greatsword, Breastplate (mk II)
Map lvl 11 starts to unlock the mk III gear (Shield, Dagger, Boots), so presumably it cycles every 5 levels.
If you skip a level, for example if you complete world 8 without exploring any level 8 maps, the next world's maps will contain the otherwise 'missed' items. So the lvl 9 map would contain 4 items (Polearm, Pants, Battleaxe, Shoulderguards) rather than the usual 2.