This makes it easier to find wilds of a certain level, rather than touching each wild individually. You can toggle between showing or not showing the level of each wilds on the world map by pinching the map with both fingers on your touch screen. These wilds can be attacked to plunder those resources or conquered to provide a bonus to the City resource production.
Wilds are the tiles arranged in a grid around your city on the world mapĮach wild is associated with a particular resource with the exception of Bogs and Plains.