With D&C 125:3 and 128:20, we have in the scriptures for everyone to see the two keys to understanding Book of Mormon geography. Interpreting the text with those two keys unlocks not only the evidence and historicity, but the meaning of many passages.
It seems only rational to realize that if the key fits, why not use it to unlock more meaning?
And if two keys fit, all the better.
Section 125 is important, but the manual does not mention it.
3 Let them build up a city unto my name upon the land opposite the city of Nauvoo, and let the name of Zarahemla be named upon it. (D&C 125:3)
There are several historical accounts that relate the intention to build a temple across the Mississippi River from Nauvoo. The two temples would face each other. One account says the site on the west was dedicated, but so far as I know, there are no official Church records documenting that dedication.