It is one of fewer than 100 surviving illustrated Mesoamerican manuscripts dating before 1600.
Also known as the Mapa de Ecatepec-Huitziltepec, the manuscript contains information about a family with the name of "de Leon," including its genealogy and land holdings.
The lands depicted in the codex stretch between modern-day Mexico City and Atoyatempan, a town in southeastern Mexico.
At the Library of Congress blog, curator John Hessler wrote, "On the one hand, the map is a traditional Aztec cartographic history with its composition and design showing Nahuatl hieroglyphics, and typical illustrations. On the other hand, it also shows churches, some Spanish place names, and other images suggesting a community adapting to Spanish rule.
"The codex shows graphically the kinds of cultural interactions taking place at an important moment in American history. In a sense, we see the birth of what would be the start of what we would come to know as the Americas."