Despite reading the wiki and other good resources, I still found the POE atlas/map dropping to be extremely confusing. I've written a summarized version that might of help to someone!
How do map drops work
- A map can drop anywhere from T1 to T#(your current map tier). e.g. if you are on a T5 map, monsters can drop T1-T5 maps.
- Magic/rare monsters can drop an additional one level higher, and bosses can drop two levels higher. e.g. the boss of a T5 map could drop anywhere from T1-T7 maps.
- Your completion bonus also gives you a chance at increasing the tier of the map, but this does not increase the maximum possible. e.g. if you have a 100% completion bonus (from 100 completed maps) and kill the boss of a T5 map, it can only drop T2-T7 maps (T1 is impossible because there's a guaranteed chance to upgrade the map).
- The only maps that can drop are ones that you have already completed or adjacent undiscovered maps.
- There is a 2x weighting for incomplete maps and a 4x weighting for adjacent maps multiplicatively; this means that an adjacent, incomplete map has a 8x chance to drop compared to other maps.
- Note that none of these rules apply to buying maps from Zana or from her missions, which can give you random maps disconnected from your completed maps.
How do Watchstones work?
- Watchstones increase the tier of all maps in their region (typically by +3 per stone) and also change the layout slightly, often revealing brand new maps.
- Maps of lower tiers are totally independent from their higher tier versions; e.g. Park T1 and Park T4 are essentially unrelated. You will not be able to drop incomplete, adjacent T5 maps from Park T1.
- A map that is not visible on the Atlas due to a Watchstone:
- Is removed from the global, completed random drop pool (you will not have that map drop anymore for any reason)
- Is not considered adjacent to any map, and thus can only drop previously completed maps
What should I do with my Watchstone (assuming I want 100% completion of all non-unique maps)?
- Slot it in a region where you have completed all non-unique maps.
- If you have multiple regions that qualify, choose the lowest tiered region (e.g. watchstone a T1-T4 region first before a T5-T8 region.
- If you still have ties, choose randomly.
But what about Conquerors?
- Getting Watchstones ASAP is critical to advancing the Atlas. As soon as you can comfortably handle beating a Conqueror and higher-tiered maps, you should hunt these out. Ignore the general rules above; go ahead and slot multiple watchstones into a single region so you can do the maps and defeat the Conqueror, then move the Watchstones back to return to regular map completion.
How do I get a specific, incomplete map to drop?
- You must grind for this on maps adjacent to the incomplete map.
- Your best bet are maps that are at least the same tier as the map you want (e.g. if you want a T7, you should grind adjacent maps that are at least T7 and not a T6) since any monster can drop the map (not just rares/bosses).
How do I stop all these low-level maps from dropping?
- Put a Watchstone in that region to prevent maps of those lower tiers from dropping.
What if I don't have enough Watchstones?
- See: "But what about Conquerors?"
