The main features of the map were placed on the grid made by the inner circle which is centered south of Genoa.
The circle is divided into sixteen equal parts. Rhumb lines connect to the points on the circle and provide a grid.
The rhumb lines on the map could be followed to navigate a vessel at sea; the grid made from them could be used to copy this portolan chart.
The five scales of distance could be used to determine distance along the rhumbs.
One compass rose is located in southwestern Africa; a second is found in the northeastern part of the map.
Can you find the compass rose and scale on the large 1489 chart?