It has never been the purpose of this website to attempt to define the geographical points described in the text. The geography of the Book of Mormon is neither completely discernable nor important. But if there is geographic description which is discernable, it must be this one. The Panamanian isthmus is accurately described in this verse and in Alma 22:32, And now, it was only the distance of a day and a half’s journey for a Nephite, on the line Bountiful and the land Desolation, from the east to the west sea…there being a small neck of land.
But even the location of this small neck has been debated. Some have argued that it is actually located in Central America, just south of the Yucatan Peninsula. This seems to complicate matters in a book which is famous for being plain and precious. What the reader should know is that Bountiful was just south of the small neck and that the land of Zarahemla was even further south.
Therefore, Moronihah had a narrow line of defense to protect their north country, but most of the Nephite cities and lands had already been captured. Moronihah was holding on by a thread, as it were.