 Portolan charts were not gridded by longitude and latitude lines, but rather by a web of compass rhumb lines, giving mariners an idea of only the distance and direction between places.By a handbook or a portolan chart, a navigator could see immediately that, for example, Pisa lay 85 miles southeast ("Scirocco" in the traditional compass rose nomenclature) of Genoa, and so a ship that set out from Genoa to Pisa would simply maintain that bearing for that distance.However, most sailing courses were not nearly that neat.