It's not clear to me that this is less costly than moving across the country. You'd have to look carefully at the network effects, but from an infrastructure pe

It's not clear to me that this is less costly than moving across the country. You'd have to look carefully at the network effects, but from an infrastructure perspective you still end up building a whole new city. In other words: what's the advantage of building San Diego II a few dozen miles from San Diego, even slowly, rather than just expanding Denver by moving people there. (Note that I agree it's better than building a new city in the middle of nowhere; the question is whether the network benefits of San Diego II can be mimicked by Denver. In this sense, I agree that countries with cities that are almost all on the coast would benefit from having high ground nearby their doomed coastal cities.)