Words of Mormon 1:13; refer in this text to 1 Ne. 3:9
“The concept of going ‘up’ when you go north and of going ‘down’ when you go south is of relatively recent origin, and thus was not used by the Nephites. When the Nephites stated they went from Nephi down to Zarahemla, they were referring to elevation and not to direction. Zarahemla was definitely lower in elevation than Nephi because the river Sidon had its head in the land of Nephi but flowed down through the center of the land of Zarahemla (Alma 16:6-7; 22:27-29).” (Daniel H. Ludlow, Companion to Your Study of the Book of Mormon, p. 169)