His mission has apparently failed in Ammonihah, so he continues on his journey to his next city. Aaron must also be a city with a political dependence upon Zarahemla. Alma is visiting the political realm of the Nephite polity, not the religious faithful for Nephite religion as they have inherited it from Lehi, Nephi, and that tradition of prophets.
Geographic: The geographic position of Aaron is not specifically stated, and the interrelationships led at least one author to assume that there must be two Aaron's. Sorenson's suggestion is that it lies to the east of Ammonihah, perhaps midway in the narrow neck of land (see Sorenson 1985, p. 204).