The map spawn under the corps of worm and bitter, which mean that most of the time, they are invisible. I have a mod that make item on ground marked and that's where I found that I only collect 10% of map that spawn.
Is there anything that I can do on my side of it's really a mod limitation ?

Interesting. I've to check how it works with worms. But biters/spitters shouldn't have any loot (maps are only added to trees, spawners, and turrets/worms), so perhaps that's why their corpses are placed over the maps?

Yes, for bitter, the problem is mainly that they cover the map dropped by the spawner. Acid also cover the map.
The way around I found today was to take a mod and reducing the decay for the alien related bodies (spawner, worms and bitter). Hightly increased the number of map found ! ^^

Could reproduce this by setting loot probability to 100%. Corpses have a final_render_layer. I haven't found such a property yet for items on ground, but if there was a way to change it, rendering maps above the corpse layer would probably help.

Did you upload your mod, or do you intend to do so? Then I could add a dependency on it until I can find a solution to fixing the rendering layer. I probably could also change the decay times myself, but why should I duplicate what another mod already does? :-)

I use a mod already here. There is plenty of option anyway when you search corpses or decay. No dependencies needed, just a warning, perhaps

I've found a very simple solution to the problem with the hidden maps: A setting that allows to mark maps with an arrow (adjustable color and display duration, optionally only in ALT-mode). A marker will only be visible to players of the force who killed the tree/spawner/worm. This should make it easy to find a map even if it's hidden by biter corpses.

Implemented in 1.0.4. Does that help?

It was super usefull, sorry for the delayed answer. but I run in an other problem : I have a bug loot mod so I installed a collecting chest mod and it takes all the map so I can never use it. Is there anyway for you to avoid being collected ? I ask the autor of the mod but it seems it will be toomutch ups intensive to add it on his side.
I use this mod : https://mods.factorio.com/mod/LootChestUPS/discussion/6069b31e72cb78d3119ca33a

Sorry, now I didn't respond for such a long time as well. :-)

I have a bug loot mod so I installed a collecting chest mod and it takes all the map so I can never use it. Is there anyway for you to avoid being collected ?

No. One mod removing loot, the other restoring it? That would be even more expensive than checking loot and not picking it up.

I ask the autor of the mod but it seems it will be toomutch ups intensive to add it on his side.

I just checked the authors code, and (without running it), I believe if it actually would run faster if it was not acting on certain items. On first glance, there also seem to be some more issues where performance of the mod could be improved (e.g. using event filters) or where things are done wrongly (e.g. when the first stack of loot has been processed, the loot inventory is cleared completely -- not just that stack).

I use this mod : https://mods.factorio.com/mod/LootChestUPS/discussion/6069b31e72cb78d3119ca33a

That mod has been deprecated in the meantime. Is there a replacement mod you're using now? Otherwise, I think I could make you a private fix for that mod …

I have a bug loot mod so I installed a collecting chest mod and it takes all the map so I can never use it. Is there anyway for you to avoid being collected ?

Became collaborator and uploaded a fix on the other end. :-)

I saw that :) Thanks !

I know. My reply here was just for the record, for people who didn't read the thread on the Loot chest board.