1920s (circa) Aviation map of United States, featuring landing fields, improved, unimproved, by Rand McNally, from the Digital Commonwealth - commonwealth 3f4639823. (<a rel="nofollow" class="external free" href="https://www.digitalcommonwealth.org/search/commonwealth:3f4639823">https://www.digitalcommonwealth.org/search/commonwealth:3f4639823</a>)
Rand McNally
Digital Commonwealth