The lack of a uniform system for the marking of navigable waters presents a serious threat to safe, international navigation. Some countries use the 'lateral system' which means that vessels proceeding in a channel in a given direction (such as from seaward to a port) are guided by seamarks of a specified type to starboard and of a different type to port, without reference to the points of the compass. Other countries use the 'cardinal system' which means that the appearance of sea marks is determined by their position - in terms of the nearest cardinal point (N, S, E or W) - with respect to the shoal they are marking.