This is one of the earliest available Policies in the game, and one of the starting two choices for Military policy (unless you play as Germany, which has an extra Military slot and will be able to use both Survey and Discipline). It is very helpful for the initial 20 or so turns, especially if you have more than one Scout. They will race through levels as they discover the world and activate Tribal Villages, or enter the occasional clash with Barbarians. If you're lucky, you could get two or even three level-ups for each Scout, which will last them throughout the game!
Civilopedia entry Edit
Even prehistoric tribes had “scouts,” those hardy individuals who went out looking for better caves, hunting grounds, and sources of water. Once folk settled down and began clumping together in villages and towns, fleet-footed and eagle-eyed individuals willing to hike over the hills and trudge through trackless forests remained of vital importance, for a civilization that doesn’t know what’s going on around it is blind to both opportunities and dangers. As they surveyed the surroundings and brought back tales of fabulous wonders, scouts not only expanded possibilities, but humanity’s imagination as well.