Before modern navigation tools, ships used portolans, nautical charts on which the ports are represented as well as many useful indications for navigation. Moreover, these cards were sometimes true works of art.
Many of us get bored when looking at a map. However, the portulans are very often spectacular and describe the maritime space as we no longer do today. Used between the 12th and 18th centuries, portulans were drawn up on parchments and were widely used by many European navigators who also contributed to their improvement after the discoveries made.
In addition to the indications of places inscribed perpendicularly along the coasts, these maritime charts make it possible to find one’s bearings on the oceans since they materialize the lines of wind (or rhumb) as a kind of grid. Thus, wind roses make it possible to locate the route and determine the course to follow. These are therefore very different maps from what we can usually see, because they are really intended for navigation.
More precisely, the portulan is constructed of sixteen rhumb lines, wind roses, sixteen nodal points and sixteen wind areas of 22° 30. The whole forms parallelograms, squares and rectangles and this has absolutely no nothing to do with the cartographic projections on which the meridians and the parallels appear.
These nautical charts are generally declined in two kinds: the basic portulans simply containing the indications of places and the information on the navigation and the others which are real colored works and presenting multiple illuminations and other artistic drawings.
Truly scholarly maps, portulans incorporate advances in cartography such as those made in terms of world measurements, although at the base, the latter are developed using rather rudimentary tools such as the compass, the sextant and the support. Nevertheless, precision is required as evidenced by the Pisane Map, which would be one of the very first portolans deforming the Mediterranean Sea by only one degree, or 90 kilometers in comparison with reality (see below).
Sources: Herodotus — National Library of France — Eden Saga