One of the Star Atlases Chen Ho used in his journey/Source from Defense Preparations Report (Wu Bei Zhi)

  The seven voyages made by Cheng Ho into the western ocean are the climax of the history of Chinese exploration and navigation. Cheng Ho was the greatest navigator in Chinese history. Known as the "San Baow Eunuch," he led a huge fleet containing thousands of people to the Western Ocean (which included today's South China Sea and part of the Indian Ocean). They sailed into the South China Sea seven times, and visited the countries nearby. The fleet then went on into the west into the Indian Ocean. They even reached Saudi Arabia and the east coast of Africa.
   Cheng Ho spent 28 years visiting 37 countries. He succeeded in opening up the sea routes, and also promoted trade between China and the western countries. His fleets were larger, and sailed further, than any other in Chinese history. They also used scientific equipment, such as the compass and astronomic charts. Cheng Ho also recorded the things he saw and the locations he passed by. He produced the most important chart of the time - the Cheng Ho Navigation Map. He also made a great contribution to the history of navigation. In order to commemorate Cheng Ho's voyages, some of the reefs and islands in the South China Sea are named after people connected with the voyages. Examples include Yung Lo Reefs (Yung Lo was the reign of the emperor at that time), Cheng Ho Reefs (Tizard Bank) and so on.