_dta:
  1.  by Jean Roth , jroth@nber.org , 9 Nov 2012
  2.  by Jean Roth , jroth@nber.org , 9 Nov 2012
  3.  by Jean Roth , jroth@nber.org , 15 Dec 2015
  4.  SAS ZIP Code Dataset ZIP file
  5.  Unique identifier is zip
  6.  Distances between ZIP that are within 25 miles

  obs:     3,764,538                          
 vars:             3                          15 Dec 2015 16:40
 size:    67,761,684                          (_dta has notes)
-------------------------------------------------------------------------------
              storage   display    value
variable name   type    format     label      variable label
-------------------------------------------------------------------------------
zip1            str5    %9s                   The 5-digit ZIP Code
zip2            str5    %9s                   The 5-digit ZIP Code
mi_to_zip       double  %10.0g                Distance between ZIP Codes that
                                                are within 25 miles
-------------------------------------------------------------------------------
Sorted by: zip1  mi_to_zip  zip2