This map was published by Gerardus Mercator in 1569 and marked a turning point in cartography. Until then, cartographers and navigators had worked independently without taking each other's needs into account. Mercator set out to find a contemporary representation of knowledge about the world and, at the same time, to make it useful for navigators. All these intentions are described in the original title of the map. New and Expanded Description of the World for the Use of Navigators, Revised and Adapted (New and more complete representation of the globe adapted for use in navigation).
The map contains a significant amount of text that aids in interpreting the map and using it for navigation. Mercator designed a new cartographic projection for this purpose, allowing sailors to use straight lines as course lines with the guarantee that these would enable them to reach the destination indicated on the map.
Although several hundred copies of this work were printed, only three complete copies remain today: one in the National Library of France, another in the Maritime Museum in Rotterdam, and this one at the University of Basel. This copy is the best preserved of the three and is the only one that is separated into 18 sheets, which gives it a larger size and greater detail (2 x 1.2 metres).
You can read more about map projections in this newsletter article: Cartographic projections: distorting the Earth in order to represent it
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