Our presentation is about Gerardus Mercator (1512-1594). Besides a cartographer, he was a calligrapher, carver and engraver on copper plates, manufacturer of scientific instruments (compasses, rules and triangles), of geographic and celestial globes and also map editor. However, it is the world-map of 1569, in a map projection different from everything else existing that moment, and that lasted for over 400 years as standard for maps, that will be, in Gerardus Mercator's universe, the main focus of this study. Throughout millenniums, one of the main issues in several societies was to understand the limits of the Universe. For the Greek people, to understand the nature was one of its main concerns and within this comprehension was the geographic world. Their “Geography” was limited to what the Greek used to call the known world or the Oikoumenë and, thus, it was this physical world the essential element to think of the meaning of cartography. A search through stars, planets, moon and sun, as well as by land, sea, rivers and mountains was the result for the demarcation of limits in their terrestrial and celestial space. Thus, philosophical ideas and concepts were essential for a new comprehension, a look around in order to understand this known world or the Oikoumenë and to be able to write and draw the shape that today is called maps or cartographic charts. In this field of investigation, procedures and ideas will be presented in order to reflectabout the historical process that several thinkers and their societies experienced, characterized by specificities, advances and regressions, as well as beliefs, philosophical concepts and images about the Earth, the Universe and man itself. And for that, contributions and main studies of astronomers, mathematics and geographers will be included, as well as analyses and critics of their predecessors. By developing this presentation about the cartographic journey of Mercator, in the History of Science context, we intend to demonstrate, mainly, how Geography enabled us to think and rethink of the limits of the known world.The increase of the space where we live depends on research projects, procedures, techniques and studies, many of which enable us to understand the world-space inhabited by different people, living in different cultures. Finally, it is essential to emphasize the importance of understanding man and its work in relation to the social context and its time.