Distances between County that are within 50 miles
Unique identifier is  county
Census Gazetteer County file
by Jean Roth , jroth@nber.org , 29 Mar 2016
Source File: counties.txt
Source File URL: http://www2.census.gov/geo/docs/maps-data/data/gazetteer/counties.zip
Source Page: http://www.census.gov/geo/maps-data/data/gazetteer1990.html
counties1990 set up by Jean Roth , jroth@nber.org , 29 Mar 2016