_dta:
  1.  gaz2015zcta5centroid set up by Jean Roth , jroth@nber.org , 4 Dec 2015
  2.  Data source : http://www2.census.gov/geo/docs/maps-data/data/gazetteer/2015_Gazetteer/2015_Gaz_zcta_national.zip
  3.  ------------------------------------------------
  4.  from http://www.census.gov/prod/cen2010/doc/sf1.pdf :
  5.  ------------------------------------------------
  6.  Internal point-
  7.  The Census Bureau calculates an internal point (latitude and longitude
  8.  coordinates) for each geographic entity. For many geographic entities,
  9.  the internal point is at or near the geographic center of the entity.
 10.  For some irregularly shaped entities (such as those shaped like a
 11.  crescent), the calculated geographic center may be located outside
 12.  the boundaries of the entity. In such instances, the internal point
 13.  is identified as a point inside the entity boundaries nearest to the
 14.  calculated geographic center and, if possible, within a land polygon.
 15.  ------------------------------------------------
 16.  by Jean Roth , jroth@nber.org , 4 Dec 2015
 17.  Census Gazetteer ZCTA5 file
 18.  Unique identifier is zcta5
 19.  Distances between ZCTA5 that are within 50000 miles

  obs: 1,098,491,592                          
 vars:             3                          4 Dec 2015 17:21
 size:19,772,848,656                          (_dta has notes)
----------------------------------------------------------------------------------------------------------------------------------------------
              storage   display    value
variable name   type    format     label      variable label
----------------------------------------------------------------------------------------------------------------------------------------------
zip1            str5    %9s                   Five digit ZIP Code Tabulation Area Census Code
zip2            str5    %9s                   Five digit ZIP Code Tabulation Area Census Code
mi_to_zcta5     double  %10.0g                Distance between ZCTAs that are within 50000 miles
----------------------------------------------------------------------------------------------------------------------------------------------
Sorted by:  zip1  mi_to_zcta5  zip2