def add_counties(data)
      foreach(data_file(USGeoData::ZCTA_COUNTY_REL_FILE), col_sep: "|") do |row|
        zcta5 = row["GEOID_ZCTA5_20"]
        county_geoid = row["GEOID_COUNTY_20"]
        overlap_land_area = row["AREALAND_PART"].to_f * SQUARE_METERS_TO_MILES