page_title: Rhumbline network
section_title: Double hexadecagon in Cantino's planisphere
hierarchical_section_title: Rhumbline network / Planispheres with double hexadecagon / Double hexadecagon in Cantino's planisphere
caption_attribution_description: English: The rhumb-line construction scheme in the Cantino planisphere
context_page_description: A rhumbline network, more properly called, a windrose network, or sometimes also called harbour-finding chart, compass chart, or rhumb chart, is a navigational aid drawn on early portolan charts dating from the medieval to early modern period. This network is like a web forming a grid on the map.
  Before accurate surveying there was no method for measuring longitude at sea so maps possessed many distortions especially in the east west direction. There was also distortion due to the curvature of the Earth's surface. The multitude of compass roses with straight lines extending outwards across the map derived from how the maps were then made by compiling empirical observations from navigators who attempted to follow a constant bearing at sea.
  To calculate a course to follow from a ships position to a point of desired destination, one would identify the winrose thought to be closest to the ships position. Then using a parallel rule — the "line of course" taken from the rose to the point of destination, would be transferred to the ships known position.
caption: Rhumb line construction scheme with two hexadecagon in the Cantino planisphere
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