How to get a time zone from a location using latitude and longitude coordinates?

Question

Given the latitude and longitude of a location, how does one know what time zone is in effect in that location?

In most cases, we are looking for an IANA/Olson time z

Answer 1

1. There are several sources online that have geojson data for timezones (here's one, here's another)

2. Use a geometry library to create polygon objects from the geojson coordinates (shapely [python], GEOS [c++], JTS [java], NTS [.net]).

3. Convert your lat/lng to a point object (however your library represents that) and check if it intersects the timezone polygon.

   from shapely.geometry import Polygon, Point
   
   def get_tz_from_lat_lng(lat, lng):
       for tz, geojson in timezones.iteritems():
           coordinates = geojson['features'][0]['geometry']['coordinates']
           polygon = Polygon(coordinates)
           point = Point(lng, lat)
           if polygon.contains(point):
               return tz