The guide uses the following color codes:
Brown is for coordinates within the island (i.e. [712324; 3416066]). Useful for locating collectibles.
Blue is for locations visited throughout the game (i.e. Coastal Forest).
Green is for all items found by Lara (both regular and secret).
Orange is for XP gained through the play.
You can read coordinates at any moment during the game; to do it, pause, view the map and set the marker on the chosen spot. For example, the above screenshot displays a location at [712336; 3416068].
Jacek "Stranger" Halas