Given a world map, you must determine the country that has the largest territory. The map is given as a String worldMap, where each character represents a square with an area of 1. Unoccupied squares are represented by space characters (' '). Occupied squares are represented by uppercase letters ('A'-'Z') that denote the occupying country. The area of a country's territory is the total area of its occupied squares. Return a String containing exactly one character - the name of the largest country. In case of a tie, return the largest country whose name comes first alphabetically.