Geography: This verse may be the most famous of all Book of Mormon geographic references, describing the general shape of two large areas connected with a “narrow neck.” A “line” divides north from south (Desolation and Cumorah north, traditional Nephite lands to the south), and this “line” runs along the narrow neck. The distance from sea to sea was “only the distance of a day and a half’s journey for a Nephite.” Sorenson suggests that a plausible distance would be 75 to 125 miles. The Isthmus of Tehuantepec is 120 miles across.
Sorenson notes other general features that are suggested by this description:
The directional trend of the two lands and the neck was generally north-south. The east sea (six references) and the west sea (twelve references) were the primary bodies of water that bounded this promised land. But notice that the key term of reference is not “land north” (only five references) but “land northward” (thirty-one references). There is, of course, a distinction; “land northward” implies a direction somewhat off from literal north. This implication that the lands are not simply oriented to the cardinal directions is confirmed by reference to the “sea north” and sea south” (Hel. 3:8). These terms are used only once, in reference to the colonizing of the land northward by the Nephites, but not in connection with the land southward. The only way to have seas north and south on a literal or descriptive basis would be for the two major bodies of land to be oriented at an angle somewhat off true north-south. That would allow part of the ocean to lie toward the south of one and another part of the ocean to lie toward north of the other.
Another important general feature of Sorenson’s interpretation of this geography is the textual requirement of a much larger west coast than east:
An east coast of 85 or so miles for the Nephite-controlled area is far shorter than the length of the land southward measured via Zarahemla and Nephi. That axis was on the order of 350 miles. The difference in these lengths is so great that it cannot be due to erroneous assumptions. The Book of Mormon text really does require that the east coast of concern to the Nephites be much shorter than the west, and any map we come up with must accommodate that fact.