In the thirteenth century a new type of chart, the portolan chart emerged. A cartographic revolution. They were created by mariners who plotted coastlines along constant compass bearings. Wind roses indicated directional bearings. Portolan charts were made to get seafarers from home to another place and back again safely. There is a great deal of detail on the coasts, but very little in the interior.

The green protrusion on the coast of Africa represents Cape Verde. The map is called “A Portuguese Nautical Map” about 1471. The mapmaker is unidentified

The next stamp shows a portion of a map in The Book of Francisco Rodrigues / Rutter of a Voyage in the Red Sea, Nautical Rules, Almanack and Maps, Written and Drawn in the East before 1515. The portolan was compiled about 1513

Though not strictly a portolan the stamp shows a portion of an anonymous Portuguese map from about 1630. The red line is the Tropic of Capricorn.