The Cartographer’s Sextant is a currency item that can be used to add a mod to a map.
There are three tiers of Cartographer’s Sextants. The Apprentice Cartographer’s Sextant can be used on maps tier 1-5. The Journeyman Cartographer’s Sextant can be used on maps tier 1-10. The Master Cartographer’s Sextant can be used on maps tier 1-15. Cartographer’s Sextants are the colors of the maps they represent. This means they are white, gold, and red respectively.
The Cartographers Sextants are very useful because they apply mods in a radius, not unlike jewels. This means you can stack a lot of mods onto maps you prefer. The only downside Sextants have is that after five uses of any map affected by the modifier, the Sextant with that modifier is consumed. Luckily, unlike Shaper’s Orbs, sextants have unlimited drops. Red tier sextants are still 4 chaos and it is controversial if they are worth using. If you get a mod such as pack size, Sextants could be worth it, but reflect or Blood Magic could be devastating. Read more about Sextants here.