General Discussion

The amount you need to live on in San Francisco, for instance, is vastly greater than in many other locations simply because rents or even mortgages are so astronomically priced.
Other areas have their own challenges to name just two:
Heating vs A/C costs
Transportation of gas from refinery to car costing more or less depending on distance and geographical considerations
Some of those things may average out over a number of years, but the real test is how far the SAME dollar will get you in Louisiana or Alabama for instance, as in LA, SF, NY, or other major urban centers.
There was a reason european countries all had different currencies (and different rates of exchange) until the Euro was dreamed up. Their micro-economies reflected those differences to some extent. The US has a single poverty level across the entire country for federal means-test purposes - RIDICULOUS!
Taxation brackets are same across the entire country for supposedly the same dollar, and the federal minimum that IIRC is still $7.50/hr are utterly inadequate just about everywhere, but most certainly in the big cities.
No politician could possibly talk authoritatively about anywhere except their own location, and everyone would be saying "Ignorant fool" because that location's numbers would not match the numbers we know.
Federal policy is irredemably broken in this, and many other, aspects.