The locations of Federal Reserve District boundaries, and of the Banks within the Districts, were determined mostly by the geographic distribution of the U.S. population at the time the Federal Reserve System was created (1913), to accommodate local needs.
Mr Trump claims the total cost of the wall will be $10bn (Â£7.5bn) to $12bn. But estimates from fact checkers and engineers seem to be universally higher. Senate Majority Leader Mitch McConnell estimated it will cost between $12-15bn, as he addressed reporters at a Republican conference in Philadelphia.
If you wanted a wall instead of a fenceâand if it truly were, as Trump has promised, 35 to 65 feet of concrete reinforced with steelâthen the costs would mount extremely fast. Imagine a 1,000-mile wall, at a height of about 50 feet, the middle of the range that Trump has thrown out.