Maps->ilvl and map lvl

Alright so few times map 'scammed' me by giving way lesser level map then area. I just went with it since it wasn't big deal. Now I went to map lvl 70 and got map lvl 66 -> from rare mob. Item level of the map is 72. So what's up with this insane difference in ilvl and actual map level? What's so different between let' say map with maplvl66&ilvl66 then this map I got which has ilvl72&maplvl66?? It's 6 levels difference. So my question is what does ilvl on map mean and what is difference between ilvl and map lvl?

Item level is a property of all items which is determined by the level of the area and rarity of the mob that dropped them: add one to the level of the area for Magic monsters, and two to the level of the area for Rare and Unique monsters.

In turn, item level determines the prefixes and suffixes which can roll on gear. In addition, each base item type has a minimum item level that it begins to drop at. For example, a Grove Bow has a required level of 35, and this is (as far as I know) also its minimum item level. However, you can get Grove Bows in maps which are as high up as item level 79, and these have a chance to roll more powerful modifiers as magic and rare items as the item level increases, as well as being able to roll a sixth socket once the item level is 50 or above.

Presently, so far as I'm aware, prefixes and suffixes on maps are presently not limited by item level but some are restricted by base map type. In the future it's possible, I might even say expected, that GGG could add some additional higher level modifiers to spice up maps that dropped in higher level areas.

The level of the area created by the map when used in the Map Device is determined by its base type rather than its item level. So in a level 70 map, you can still have lower base types of maps drop (anything from 66 to 72), though these will (somewhat meaninglessly for now) still have item level 70 to 72.

The upshot of this is that gaining XP eventually becomes a somewhat erratic process as you are unlikely to maintain a stable base of higher (area) level maps forever. By using Alchemy and Chaos orbs to optimise the item quantity on maps 70 and above, you can prolong your stay in the higher tiers, and some players will even spend Regal and Exalted orbs trying to make a level 77 map absolutely perfect before using it.

My present hope is that eventually this erratic gain in experience is eventually made up for by a wide variety of modifiers which keep even low level maps interesting and fun to play in the endgame, even in the absence of much XP to be had in them. Presently, the mods which are available do increase the difficulty and change the experience quite a bit, but there's much more which could be done here to make the experience different each time, and force players into making interesting decisions about which skills to equip when entering each map.

Kind of off topic, but in the patch that's coming out soon, they're going to add some new modifiers up to ilvl 79. Pretty sweet.