View Source TzWorld

Resolve timezones from a location using data from the timezone-boundary-builder project.


Add tz_world to your list of dependencies in mix.exs:

def deps do
    {:tz_world, "~> 1.2.1"}

After adding TzWorld as a dependency, run mix deps.get to install it. Then run mix tz_world.update to install the timezone data.

NOTE No data is installed with the package and until the data is installed with mix tz_world.update all calls to TzWorld.timezone_at/1 will return {:error, :time_zone_not_found}.


There is no mandatory configuration required however three options may be configured in config.exs:

config :tz_world,
  # The default is the `priv` directory of `:tz_world`
  data_dir: "geodata/directory",
  # The default is either the trust store included in the
  # libraries `CAStore` or `certifi` or the platform
  # trust store.
  cacertfile: "path/to/ca_trust_store",
  # The default is no options, however one can set any `httpc` client options.
  httpc_opts: [
    proxy: {{String.to_charlist(proxy_host), proxy_port}, []}

Backend selection

TzWorld provides alternative strategies for managing access to the backend data. Each backend is implemented as a GenServer that needs to be either manually started with BackendModule.start_link/1 or preferably added to your application's supervision tree.

The recommended backend is TzWorld.Backend.EtsWithIndexCache unless the host system is memory constrained in which case TzWorld.Backend.DetsWithIndexCache is recommended.

For example:

defmodule MyApp.Application do
  @moduledoc false

  use Application

  def start(_type, _args) do
    children = [

    opts = [strategy: :one_for_one, name: MyApp.Supervisor]
    Supervisor.start_link(children, opts)

The following backends are available:

  • TzWorld.Backend.Memory which retains all data in memory for fast (but not fastest) performance at the expense of using approximately 1GB of memory

  • TzWorld.Backend.Dets which uses Erlang's :dets data store. This uses negligible memory at the expense of slow access times (approximately 500ms in testing)

  • TzWorld.Backend.DetsWithIndexCache which balances memory usage and performance. This backend is recommended in most situations since its performance is similar to TzWorld.Backend.Memory (about 5% slower in testing) and uses about 25Mb of memory

  • TzWorld.Backend.Ets which uses :ets for storage. With the default settings of :compressed for the :ets table its memory consumption is about 512Mb but with access that is over 20 times slower than TzWorld.Backend.DetsWithIndexCache

  • TzWorld.Backend.EtsWithIndexCache which uses :ets for storage with an additional in-memory cache of the bounding boxes. This still uses about 512Mb but is faster than any of the other backends by about 40%

Installing the Timezones Geo JSON data

Installing tz_world from source or from hex does not include the timezones Geo JSON data. The data is required and to install or update it run:

mix tz_world.update

This task will download, transform, zip and store the timezones Geo data. Depending on internet and computer speed this may take a few minutes.

By default mix tz_world.update will download geojson data that does not include time zone information for the oceans. There are two optional parameters that are accepted by mix tz_world.update that can be used to configure the desired behaviour:

  • --include-oceans will download the geojson data, including data for the oceans. This give almost complete global coverage of time zone data. The default is --no-include-oceans which does not include data that covers the oceans. The geojson data including the oceans is about 10% larger than the data that does not include the oceans.

  • --force will force an update to the geojson data even if the installed data is the latest release. This option can be useful if you choose to switch from the data without ocean coverage to the data with ocean coverage (and the reverse). The default is --no-force.

Updating the Timezone data

From time-to-time the timezones Geo JSON data is updated in the upstream project. The mix task mix tz_world.update will update the data if it is available.

A running application can also be instructed to reload the data by executing TzWorld.reload_timezone_data.


The primary API is TzWorld.timezone_at. It takes either a Geo.Point struct or a longitude and latitude in degrees. Note the parameter order: longitude, latitude. It also takes and optional second parameter, backend, which must be one of the configured and running backend modules. By default timezone_at/2 will detect a running backend and will raise an exception if no running backend is found.

iex> TzWorld.timezone_at(%Geo.Point{coordinates: {3.2, 45.32}})
{:ok, "Europe/Paris"}

iex> TzWorld.timezone_at({3.2, 45.32})
{:ok, "Europe/Paris"}

iex> TzWorld.timezone_at(%Geo.PointZ{coordinates: {-74.006, 40.7128, 0.0}})
{:ok, "America/New_York"}

# Assumes that the downloaded data does not include
# data for the oceans (the default)
iex> TzWorld.timezone_at(%Geo.Point{coordinates: {1.3, 65.62}})
{:error, :time_zone_not_found}