Maps are inhibitated by different monster "familys" or groups , meaning for example if you are casting with your ice charms on warlock , you should NOT do Arctic maps. There is a coldimmune monster on these arctics. Or if you use lightnings to cast you wanna avoid electriver maps , there is a lightimmune/lightabsorber mob , and so on. Can be used as an advantage to regular mazes where all mobs accur , specially as newer player or with weaknesses / not fully geared
Also you do not have monsters on turns or already explored spots , which makes you finish the map quicker, killing less trashmobs (leveling slower) , more chance of good drops from evils/quests within fewer levels.
As already says, no spins, no trapdoors no wells .
Due the maps Mosterlevel cap you can play the map "on the cap" and always have a steady monsterlevel , like Verdun sayd, to farm specific tiers - mostly useful for skillers -OR SELLERS !
Also maps can have bonuses like +Guildpoints or +Level up when completed , or stats like +Monster difficulty which should yield more/better quality items.. or + Experience gained , and so on.
here it may be helpful :
Tier----Quality-------Level Req--------Max Monster Level-----Map Size
1(I)-----Patched-----------0--------------------15---------Opener Level
2(II)----Rawhide-----------0--------------------20------------11x12
3(III)---Tanned------------0--------------------25------------12x14
4(IV)----Cured-------------5--------------------30------------13x16
5(V)-----Hard-------------10--------------------35------------14x18
6(VI)----Double cured-----15--------------------40------------15x20
7(VII)---Rigid------------20--------------------45------------16x22
8(VIII)--Embossed---------25--------------------50------------17x24
9(IX)----Imbued-----------30--------------------55------------18x26
10(X)----Runed------------35--------------------60------------19x28
11(XI)---Enchanted--------40--------------------65------------20x30
12(XII)--Tempered---------45--------------------70------------21x32
13(XIII)-Encrested--------50--------------------75------------22x34
14(XIV)--Fine honed-------55--------------------80------------23x36
greetings