So, 1500 miles on a side AND 1500 miles tall, and ~ 200+ feet THICK.15 And he that talked with me had a golden reed to measure the city, and the gates thereof, and the wall thereof.
16 And the city lieth foursquare, and the length* is as large as the breadth: and he measured the city with the reed*, twelve thousand furlongs. The length and the breadth and the height of it are equal.
17 And he measured the wall thereof, an hundred and forty and four cubits, according to the measure of a man, that is, of the angel.
Explanation 1: Symbolic language is being used. All of the measurements are a factor of 12, multiplied by 1000 for the dimensions or squared for the thickness. I don't see what the significance of the symbolism would be, and there is emphasis that angel cubits are equal to human cubits. Also, I have seen the maps of the 1500 mile square centered on Independence, MO or thereabouts, and I am inclined to believe this is intended literally.
Explanation 2: It is literal. It is unthinkable that a physical wall would be built that high which would extend well into space. However, I think a force field of some type is entirely likely. I have heard a lot of anecdotal cases of people who have dreamed or envisioned a nuclear attack on Zion, and the nuclear missiles being stopped or disabled by the power of the priesthood. I just Googled, and ICBMs reach a maximum altitude between 500 and 750 miles, so the 1500 mile height makes a lot of sense in that regard.
I wonder if it will be some kind of force field of faith, or if it will be some kind of literal technological force field or field of some kind that would knock out a missile (or a bomber jet for that matter). I tend to believe it would be a literal tech force field of some kind. I think of the earthen barriers thrown up by the Nephites to repel the Lamanites - I see such actions as a exercise of priesthood power - i.e. the priesthood foresaw the need, but almost unimaginable human effort had to go into the preparation. I'm not saying that being in a prayer circle or just raising your arm to the square would do the job if that were God's will. But I don't think we should assume that.
I'd love to hear some scientific minded folks, (paging BroJones!) discuss the feasibility of such a force field. Maybe it wouldn't be up all the time but would just activate and disable a bomber or a bomb/missile when one was detected.
Maybe there are other explanations than the two above, although I think literal/not literal probably covers the binary, but maybe there are some ideas of what a symbolic interpretation might mean? Other ideas on a literal solution?