This is exactly right and it works both ways. If you're comparing NYC to St. Louis and desire a 60th floor apartment in a high rise, then the COL difference is

This is exactly right and it works both ways. If you're comparing NYC to St. Louis and desire a 60th floor apartment in a high rise, then the COL difference is infinity or mu or NAN or something. You simply can't make the comparison. The same is true when comparing the average detached home in the Midwest to San Francisco. For most people, the answer to, "how much more would I have to make to buy the same house out there?" is "it doesn't matter, because you'll never make that much."