What is a nautical chart, really? Uncovering the geometry of early modern nautical charts

During the sixteenth century and beyond, nautical charts were the single most important source of geographical information for the image of the world that was depicted in European maps and atlases. However, little was known until very recently about the geometry of these remarkable artefacts. Making use of results obtained with modern techniques of cartometric analysis and numerical modeling, we clarify the nature of the early modern nautical chart and show how its geometry is intimately connected with the contemporaneous navigational methods. Two major conclusions follow from our study: firstly, nautical charts can only be understood in full cognizance of the navigational techniques they were intended to support; and secondly, nautical charts were instruments for navigation, not attempts at representing the Earth.