In brief
Historic Mexico City was built over Tenochtitlan and preserves pre-Hispanic and colonial layers. Xochimilco adds canals and artificial islands to the shared heritage property.
Useful to know
Historic Mexico City was built over Tenochtitlan and preserves pre-Hispanic and colonial layers. Xochimilco adds canals and artificial islands to the shared heritage property. [1]
These represent different spatial organizations. Compare the dense centre with the water system rather than seeking one common facade feature. Their shared inscription does not make them a single adjacent square.
Sources
For further detail and to check the information: