The map in Miasmata does not update itself automatically. The player has to use the in-game Cartography system to sight bearings on known landmarks in order to triangulate their location, as well as the location of objects in the distance. When this is done, the game map is then extended or 'revealed' around the player's current position.
Furthermore you will find partial maps in huts and tents which reveal locations of the most valuable plants. Those are needed for synthesizing drugs for lasting effects as well as The Cure. The mentioned areas become instantly marked on your map with a circle. It is strongly recommended to search those circled areas for any "special" plants (and store them in the storage bins) while you're in the area, to avoid long treks across the island. Beware of The Creature, because it tends to guard especially these locations.
Using a Mental Clarity Tonic will 'sight' your position on the game map as long as it is active. This does not allow your position to be 'known' or reveal the map unless you use cartography. It has been said that enhancing your mental abilities also has the effect (asides from the obvious) of expanding the amount of map that is revealed when triangulation is successful.