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

https://en.wikipedia.org/wiki/Great-circle_distance

And here is a good implementation using JSON data: https://github.com/agap/llttz

public TimeZone nearestTimeZone(Location node) {
    double bestDistance = Double.MAX_VALUE;
    Location bestGuess = timeZones.get(0);

    for (Location current : timeZones.subList(1, timeZones.size())) {
        double newDistance = distanceInKilometers(node, current);

        if (newDistance < bestDistance) {
            bestDistance = newDistance;
            bestGuess = current;
        }
    }

    return java.util.TimeZone.getTimeZone(bestGuess.getZone());
}

  protected double distanceInKilometers(final double latFrom, final double lonFrom, final double latTo, final double lonTo) {
        final double meridianLength = 111.1;
        return meridianLength * centralAngle(latFrom, lonFrom, latTo, lonTo);
    }

    protected double centralAngle(final Location from, final Location to) {
        return centralAngle(from.getLatitude(), from.getLongitude(), to.getLatitude(), to.getLongitude());
    }

    protected double centralAngle(final double latFrom, final double lonFrom, final double latTo, final double lonTo) {
        final double latFromRad = toRadians(latFrom),
                lonFromRad = toRadians(lonFrom),
                latToRad   = toRadians(latTo),
                lonToRad   = toRadians(lonTo);

        final double centralAngle = toDegrees(acos(sin(latFromRad) * sin(latToRad) + cos(latFromRad) * cos(latToRad) * cos(lonToRad - lonFromRad)));

        return centralAngle <= 180.0 ? centralAngle : (360.0 - centralAngle);
    }

    protected double distanceInKilometers(final Location from, final Location to) {
        return distanceInKilometers(from.getLatitude(), from.getLongitude(), to.getLatitude(), to.getLongitude());
    }
}