To prepare the sea chart, the cartographer begins by drawing a rectangle twice as wide as high. He then plots the two central axes and divides them into equal intervals: 18 on the vertical axis and 36 on the horizontal. Next, he draws the entire grid of meridians and parallels. Waldseemüller (ca. 1470-ca. 1520) confined his attention to the section of the grid extending 240° in longitude between latitude 70° north and latitude 50° south. The grid is only a construction diagram and so does not appear on the actual map. Waldseemüller then traced a circle with a radius equal to the vertical semi-axis and marked the wind directions in accordance with the standard compass design, plotting 16 points on the circumference. On each of these points he drew a new wind rose with 16 directions—and so on until he had filled the entire grid of navigational rhumb lines. The North, South, East, and West winds are shown on the cardinal directions, while the diagonals indicate the North-East, South-East, South-West, and North-West winds. This grid of radiating spokes—the rhumb lines—provides a reliable guide for plotting navigation routes, which are shown as lines parallel to a given direction on the wind rose.