Generally speaking, the US population is quite concentrated. 66% of people live with-in 100mi (160km) of a border:

* https://www.aclu.org/other/constitution-100-mile-border-zone

A sizeable portion live on the coast:

> As of 2014, nearly 40% of the population lived in counties on the coast.

* https://oceanservice.noaa.gov/facts/population.html

So presumably there's a decent amount of space 'in the middle'.