There are just two kinds of chest that can appear in the world map; the Normal Chest and the Multichest.
Normal chest: These chests contain up to 5 gems. Make sure to check your World Map several times a day, because these chests reappear from time to time.
Multichest: These fabulous chests can only be obtained when reaching certain points in the different paths that depart from your city. They contain awesome quantities of resources, and they will be very useful at certain points during your travels.