According to the Zarahemla Research Foundation, while abridging from the large plates of Nephi, Mormon inserts what is the main reference on geography in the entire Book of Mormon (Alma 27:27-34). It is significant because it is the only place which describes all the major lands and their relationship to each other. At the beginning of the passage Mormon notes that "the king [of the Lamanites] sent a proclamation throughout all the land, amongst all his people who were in all his land" (Alma 22:27). He then proceeds to describe and relate the geography of the Nephites and Lamanites with that of the Jaredites and People of Zarahemla. At the end of this passage, Mormon repeats the information from Alma 22:27 by declaring: "The king of the Lamanites sent a proclamation among all his people" (Alma 23:1). Thus Mormon is using a Hebrew writing device called epanalepsis, or resumptive repetition, which clearly highlights that everything in between is added by him.
In the past, internal geographical information was discounted because of the great upheaval of the land during the time of the crucifixion of Christ (3 Nephi 8:11-12, 17). It was surmised that any descriptions given before the upheaval were no longer valid, making identification of lands and cities impossible. But Mormon was the abridger. As such, he was responsible for most of the nearly 400 geographic references. Mormon was also the leading general of his time, which means that he was also an authority on geography. From this we must conclude that the references are accurate and purposeful. [Zarahemla Research Foundation, "Introduction to Geography" in The Book of Mormon: Restored Covenant Edition, p. 997]
“The King of the Lamanites Sent a Proclamation Among All His People”
According to Raymond Treat, Mormon was abridging from the large plates of Nephi when he paused in his work of editing and inserted the geographic description of Alma 22:27-34. This becomes clear if we compare Alma 22:27 and Alma 23:1:
And it came to pass that the king sent a proclamation throughout all the land, amongst all his people . . . (Alma 22:27)
Behold, now it came to pass that the king of the Lamanites sent a proclamation among all his people . . . (Alma 23:1)
The verses are the same. After engraving the first part of Alma 22:27 from the large plates, Mormon inserted his own information on geography and then picked up the account from the large plates by repeating the same passage in 23:1. This means that all the information between these two verses was written by Mormon.
In addition, it should be pointed out that almost 400 geographical references in the Book of Mormon passed across the "desk" of the editor, Mormon. Mormon had the expertise to know whether these references were still valid at the time he was working on the abridgment more than 300 years after the upheaval.
But why did Mormon insert his major references to geography? There are several possibilities to consider:
1. To aid the Gentiles in locating the remnant of Lehi.
2. To locate the hill Cumorah.
3. To provide a historical base similar to the Bible. Mormon knew that to consider this record an allegory would condemn it and make it as useless as if it were a fraud. (see 1 Nephi 22:1-3)
4. To enrich the understanding of the reader.
Geography is a valid and timely subject. We should no longer relegate it to a secondary position but recognize that we have a clear mandate to pursue this topic. [Raymond C. Treat, "Mormon's Hidden Message," in Recent Book of Mormon Developments, Vol. 2, pp. 142-143]