[bane]

You're only counting those areas specific GDPs. But I bet if you look at the components of GDP they contribute to by making markets available to the rest of the country (for example) it's far higher.

For example, NYC is home to much of the publishing industry. But all those books go out to local bookstores where they are sold at a small profit, increasing the GDP of those local areas above and beyond NYC's publishing industry's contribution.