We shall see later on how this error helped the progress of geographical discovery.
The total addition of these mediaeval travels to geographical knowledge consisted mainly in the addition of a wider extent of land in China, and the archipelago of Japan, or Cipangu, to the map of the world.
The accompanying map displays the various travels and voyages of importance, and will enable the reader to understand how students of geography, who added on to Ptolemy's estimate of the extent of the world east and west the new knowledge acquired by Marco Polo, would still further decrease the distance westward between Europe and Cipangu, and thus prepare men for the voyage of Columbus.
[_Authorities:_ Sir Henry Yule, _Cathay and the Way Thither_, 1865; _The Book of Ser Marco Polo_, 1875.].