Conversation so far:
What kind of sailing charts did Zheng He create?
Zheng He's sailing charts, the Mao Kun map, were published in a book entitled the Wubei Zhi.
Did Zheng He use his sailing charts to map out the ocean?
The Mao Kun Map covers the Indian Ocean including South India, Sri Lanka, the Maldives, and East Africa.
Was Zheng He the first person to map the Indian Ocean?
The reports of the explorers of Ptolemaic Egypt resulted in the best maps of the region until the Portuguese era many centuries later.
Did Zheng He work alone or with others to create his sailing charts?
Analysis suggests that Arabic-speaking pilots with a detailed knowledge of the African coast were involved in the cartography.
What was Zheng He's most important achievement with the sailing charts?
The sailing instructions are given using a 24-point compass system with a Chinese symbol for each point.

Question: What else is different about these sailing charts that makes them different than a formal map?
Self-contained rewrite: What else is different about Zheng He's sailing charts that makes them different than a formal map?