Mapping US zip code to time zone

Question

When users register with our app  we are able to infer their zip code when we validate them against a national database   What would be the best way to determine a good potential guess of their time zone from this zip code   We are trying to minimize the amount of data we explicitly have to ask them for   They will be able to manually set the time zone later if our best guess is wrong   I realize zip codes won t help with figuring out the time zone outside the US  but in that case we d have to manually ask anyway  and we deal predominantly with the US regardless   I ve found a lot of zip code databases  and so far only a few contain time zone information  but those that do are not free  such as this one   If it s absolutely necessary to pay a subscription to a service in order to do this  then it will not be worth it and we will just have to ask users explicitly   Although language isn t particularly relevant as I can probably convert things however needed  we re using PHP and MySQL

User · Answer

In addition to Doug Kavendek answer  One could use the following approach to get closer to tz database    Download  Free Zip Code Latitude and Longitude Database  Download  A shapefile of the TZ timezones of the world  Use any free library for shapefile querying  e g   NET Easy GIS  NET  LGPL          var shapeFile   new ShapeFile shapeFilePath       var shapeIndex   shapeFile GetShapeIndexContainingPoint new PointD long  lat   0D       var attrValues   shapeFile GetAttributeFieldValues shapeIndex       var timeZoneId   attrValues 0     P S  Can t insert all the links    So please use search

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This will download a yaml file that will map all timezones to an array of their zipcodes   curl https   gist githubusercontent com anonymous 01bf19b21da3424f6418 raw 0d69a384f55c6f68244ddaa07e0c2272b44cb1de timezones to zipcodes yml  gt  timezones to zipcodes yml   e g    Eastern Time  US  amp  Canada     gt    00100    00101    00102    00103    00104         Central Time  US  amp  Canada     gt    35000    35001    35002    35003    35004        etc      If you prefer the shortened timezones  you can run this one   curl https   gist githubusercontent com anonymous 4e04970131ca82945080 raw e85876daf39a823e54d17a79258b170d0a33dac0 timezones to zipcodes short yml  gt  timezones to zipcodes yml   e g    EDT    gt    00100    00101    00102    00103    00104         CDT    gt    35000    35001    35002    35003    35004        etc

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See these links for the Olson database    http   en wikipedia org wiki Tz database ftp   ftp iana org tz tz-link html  yes  ftp   http   www twinsun com tz tz-link htm  ftp   ftp iana org tz releases  ftp   elsie nci nih gov pub   https   iana org time-zones

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I created an Open-Source  MIT licensed  MySQL database table that cross-references zip codes and timezones and uploaded it to sourceforge net   http   sourceforge net projects zip2timezone files    It is sourced from four locations  primary Yahoo PlaceFinder API - thanks  Chris N   See the README file for more information and instructions

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There s actually a great Google API for this  It takes in a location and returns the timezone for that location  Should be simple enough to create a bash or python script to get the results for each address in a CSV file or database then save the timezone information   https   developers google com maps documentation timezone start  Request Endpoint   https   maps googleapis com maps api timezone json location 38 908133 -77 047119 amp timestamp 1458000000 amp key YOUR API KEY   Response         dstOffset    3600      rawOffset    -18000      status     OK       timeZoneId     America New York       timeZoneName     Eastern Daylight Time

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Also note  that if you happen to be using Yahoo geocoding service you can have timezone information returned to you by setting the correct flag   http   developer yahoo com geo placefinder guide requests html flags-parameter

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If you want  you can also get a feel for the timezone by asking the browser Josh Fraser has a nice write up on it here  var rightNow   new Date    var jan1   new Date rightNow getFullYear    0  1  0  0  0  0   var temp   jan1 toGMTString    var jan2   new Date temp substring 0  temp lastIndexOf     -1    var std time offset    jan1 - jan2     1000   60   60     The second thing that you need to know is whether the location observes daylight savings time  DST  or not  Since DST is always observed during the summer  we can compare the time offset between two dates in January  to the time offset between two dates in June  If the offsets are different  then we know that the location observes DST  If the offsets are the same  then we know that the location DOES NOT observe DST   var june1   new Date rightNow getFullYear    6  1  0  0  0  0   temp   june1 toGMTString    var june2   new Date temp substring 0  temp lastIndexOf     -1    var daylight time offset    june1 - june2     1000   60   60   var dst  if  std time offset    daylight time offset        dst    0      daylight savings time is NOT observed   else       dst    1      daylight savings time is observed     All credit for this goes to Josh Fraser   This might help you with customers outside the US  and it might complement your zip approach   Here is a SO questions that touch on getting the timezone from javascript

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Google has a specific API for this  https   developers google com maps documentation timezone   eg  https   maps googleapis com maps api timezone json location 40 704822 -74 0137431 amp timestamp 0      dstOffset  0    rawOffset  -18000    status   OK     timeZoneId   America New York     timeZoneName   Eastern Standard Time      They require a unix timestamp on the querystring  From the response returned it appears that timeZoneName takes into account daylight savings  based on the timestamp  while timeZoneId is a DST-independent name for the timezone   For my use  in Python  I am just passing timestamp 0 and using the timeZoneId value to get a tz info object from pytz  I can then use that to localize any particular datetime in my own code   I believe for PHP similarly you can find  America New York  in http   pecl php net package timezonedb

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Most states are in exactly one time zone  though there are a few exceptions    Most zip codes do not cross state boundaries  though there are a few exceptions   You could quickly come up with your own list of time zones per zip by combining those facts  Here s a list of zip code ranges per state  and a list of states per time zone  You can see the boundaries of zip codes and compare to the timezone map using this link  or Google Earth  to map zips to time zones for the states that are split by a time zone line  The majority of non-US countries you are dealing with are probably in exactly one time zone  again  there are exceptions    Depending on your needs  you may want to look at where your top-N non-US visitors come from and just lookup their time zone

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I just found a free zip database that includes time offset and participation in DST   I do like Erik J s answer  as it would help me choose the actual time zone as opposed to just the offset  because you never can be completely sure on the rules   but I think I might start with this  and have it try to find the best time zone match based on offset dst configuration   I think I may try to set up a simple version of Development 4 0 s answer to check against what I get from the zip info as a sanity test   It s definitely not as simple as I d hope  but a combination should get me at least 90  sure of a user s time zone

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I ve been working on this problem for my own site and feel like I ve come up with a pretty good solution  1  Assign time zones to all states with only one timezone  most states   and then either  2a  use the js solution  Javascript PHP and timezones  for the remaining states  or  2b  use a database like the one linked above by  Doug   This way  you can find tz cheaply  and highly accurately   for the majority of your users and then use one of the other  more expensive methods to get it for the rest of the states   Not super elegant  but seemed better to me than using js or a database for each and every user

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Ruby gem to convert zip code to timezone  https   github com Katlean TZip  forked from https   github com farski TZip     gt  ActiveSupport  TimeZone find by zipcode  90029      gt   Pacific Time  US  amp  Canada     It s fast  small  and has no external dependencies  but keep in mind that zip codes just don t map perfectly to timezones

[timezone] Mapping US zip code to time zone

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