You start with an overgrown island filled with wilderness that prevents you from placing anything. As you level up, slowly the wilderness will be cleared, alternating North and East sides of your Build Area.
Also look for small "channels" in the Wilderness that while not large enough to place full buildings, will let you place small footprint Decorations --like cows, horses and goats.
Land is a purposely limited resource.
Also note that Water Areas also unlock with levelling, allowing placement of items (like the Colossus or the Dolphin).