Maps, like works of art and literature, are a means of communication. In fact, when we look at a map we say that we are "reading" it. While we usually think of maps as records of geographical data, they may also record and communicate ideas and even legend and scripture. Medieval world maps of the three continents or the climatic zones were based on Biblical narrative and literary sources rather than on observation and experience.
In the fifteenth century, the rediscovered Geography of the Greek mathematician Ptolemy was first translated into Latin and had a powerful impact on Renaissance cartographers. Gradually, and with increasing accuracy, maps came to represent geographic reality.
The geographical writings of Ptolemy summed up nearly six centuries of Greek speculation on the shape of the earth and the extent of its habitation. Ptolemy stated that the earth was spherical and demonstrated that places upon it could be located within a geographical coordinate system. Most importantly, Ptolemy recognized the problems of depicting a spherical earth on a flat surface and developed three solutions, or projections, for doing so. Within a century of Ptolemy’s death, his work was virtually forgotten. It was not until the fourteenth century that manuscripts of his Geography preserved in Constantinople became known in Europe. Renaissance cartographers eagerly adopted Ptolemy’s concept of ordering space, of representing a subject within a measured geometrical framework.
Ironically, Ptolemy’s work became known in Europe just at the time that explorers would demonstrate its limitations. Early in the sixteenth century, editions of Ptolemy began to incorporate maps reflecting new discoveries. The original maps were retained in "their ancient form," but for the first time a distinction was made between ancient and modern geography. New maps began to give Renaissance readers a sense of the size of the world and provided pictures of lands previously unknown.