Geographic: The land Bountiful is the northernmost holding of the Nephites at this point in their history. This description of the land Bountiful was given in Alma:
Alma 22:29-30
29 And also there were many Lamanites on the east by the seashore, whither the Nephites had driven them. And thus the Nephites were nearly surrounded by the Lamanites; nevertheless the Nephites had taken possession of all the northern parts of the land bordering on the wilderness, at the head of the river Sidon, from the east to the west, round about on the wilderness side; on the north, even until they came to the land which they called Bountiful.
30 And it bordered upon the land which they called Desolation, it being so far northward that it came into the land which had been peopled and been destroyed, of whose bones we have spoken, which was discovered by the people of Zarahemla, it being the place of their first landing.
The Land Bountiful is the northernmost holding of the Nephites, and it controls, and apparently straddles, the narrow neck of Land. The verses from Alma place the most northern border of the land Bountiful up to the land Desolation, which was the inhabitance of the Jaredites.
When the Nephites fortify their land “against the Lamanites, from the west sea, even unto the east” they are apparently drawing their defensive line across the most narrow part of the land. Militarily, they have forfeited the land of Zarahemla, and are retreated to the last defensive line, a line not breached by the Lamanites in the past.
Helaman 7 is dealing with a distance involving the narrow neck of land, and lists that distance as “a day’s journey for a Nephite.” Earlier, we have another description of time-distance for the narrow neck of land from Alma:
Alma 22:32
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; and thus the land of Nephi and the land of Zarahemla were nearly surrounded by water, there being a small neck of land between the land northward and the land southward.
We now have two different time distances, one being a day’s journey and one a day and a half’s journey. Neither geographic statement explicitly mentions that it is a “sea to sea” measurement, though that may be easily implied by both statements. It is most probable that they are measuring a different point, and thus we have different measurements. This particular measurement in Helaman is “on the line which they had fortified and stationed their armies to defend their north country.” In the case of this smaller distance, it may be measuring to the area later called the land of Joshua (Mormon 2:6) (Sorenson, John L. The Geography of Book of Mormon Events. FARMS 1990, p. 303).