-man.

-MĀN locative suffix [(2)Cf.56V]. This appears to be derived from MAN(I) ‘to extend over a surface,’ but both attestation in C ĀCŌLMĀN and ŌZTŌMĀN, have a specifically marked long vowel. Unlike a postposition, this combines only with full stems, not with possessive prefixes.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 135.

-mān = ending of place names
Horacio Carochi, S.J., Grammar of the Mexican language with an explanation of its adverbs (1645), translated and edited with commentary by James Lockhart, UCLA Latin American Studies Volume 89 (Stanford: Stanford University Press, UCLA Latin American Center Publications, 2001), 506.