Ruby gem for finding timezone of location

You can make your own calls to a geolocation service, like Google Maps to translate City, State into latitude and longitude. There are also open database seeds that will give you latitude and longitudes for cities around the world. You could make a location model and seed that table with one of those.

Here is one place you can download geolocation data for free: http://www.maxmind.com/app/geolitecity

Check this gem: https://github.com/sck-v/google_timezone

It uses google timezone api to determine timezone by known latitude and longitude

You can easily get a latitude and longitude using the google maps geocoding API. There are ruby implementations for the API like GeoKit. Once you have that you can use the timezone gem to easily get the timezone of a latitude and longitude. The gem makes it easy to do time conversions in your timezone as well.

Here is an example using GeoKit and TimeZone.

require 'geokit'
require 'timezone'

res = Geokit::Geocoders::GoogleGeocoder.geocode('140 Market St, San Francisco, CA')
timezone = Timezone::Zone.new(:latlon => res.ll)

timezone.zone
=> "America/Los_Angeles"
timezone.time Time.now
=> 2011-12-01 14:02:13 UTC

For the second part of the question, see the accepted answer to this question:

Determine timezone from latitude/longitude without using web services like Geonames.org

As stated in that answer, you should:

• Download the database of cities from geonames.org
• convert it to a compact lat/lon -> timezone list
• use an R-Tree implementation to efficiently lookup the nearest city (or rather, its timezone) to a given coordinate

Keep in mind also that many U.S. states belong to a single time zone, which should make the job easier.