OK, I get it. Most of the US is one big grid. There are natural boundaries (large lakes, mountain ranges, large national or state parks, etc.) that interrupt the US grid, but only states that have these features, or are the most sparsely populated have “grid edges.” I live in the former, and somewhat in the latter for my home state, California.
Isn’t California the most populous state? Yes, at almost 40 million people, but it’s also a very large state (Texas and Alaska are larger). Also, the population is concentrated in 4 very high-density metro areas (, and 10 to 15 cities that range from just over 500,000 to over 150,000. None of the above heavily populated areas are north of The Sacramento Metro Area nor East of the Central Valley. That leaves many areas with little or no grid, and plenty of grid-edges.
This paper is about methods used to harden the grid at these grid-edges.