it leads to a cool spider cave, with ores and mushrooms in them (the ore looked purple/crystal), not sure what else the map is still for. i bet you can trash it, but don't take my word for it , if u feel unsafe about it.

For anyone that's deleted the map:

The map leads to a cool spider cave that is mainly there to excite explores a little. The cave is well made, but contains little of real value. You do not need the map to enter or find the cave, but it will make it easier. The map can probably be discarded without problems.

I went into the cave and counted the resources inside. The cave mainly contains sapphire and some other medium-rare ore veins, some of which are quite well-hidden. Next to this, the cave also contains 2 treasure chests that can be opened with a key (bronze, silver...). For me, both chests yielded me a black stone (weapon) when opened with a silver key, but this is probably RNG. Next to the ore veins, the cave also contains some mushrooms. Noteworthy is that a trade item (Medicinal Autumn Bellflower, 1,200 silver) can be gathered here, although I do not really understand why as you probably are exploring on foot, and as such, will be slowed down significantly by picking this item up. Finally, for some reason many of the, seemingly sapphire, mineral veins are also unreachable or not mine-able, maybe they are there for decoration?

Here is a summary of what I found:

Ore/mineral veins
Sapphire 16
Feldspar 6
Silver 6
Beryl 2
Gold 2
Coal 2
Bryophite 4
Topaz 2

Non-mine-able:
Sapphire 9

Herbs/Mushrooms:
Fog Mushroom 2
Cloud Mushroom 3
Ghost Mushroom 1
Sky Mushroom 3
Bluffer Mushroom 2
Wild Herb 5-9
Autumn Bellflower 1 (trade item)

Miscellaneous:
Treasure Chest 2
Some small gatherable "trash items" yielding EXP or LUCK scrolls and the like.

It's an quest reward. However this item isn't required to open this quest, but you should at least finished the quest where you should put the map pieces together.
https://bdocodex.com/jp/quest/3034/1