Custom map providers

Decidim can be configured to use multiple different map service providers but it can be also extended to use any possible service provider out there.

If you want to create your own provider integration, you will need to find a service provider that provides all the following services:

A geocoding server in order to turn user entered addresses into geocoordinates.
A geocoding autocompletion server in order to suggest and predict addresses based on the user input and turning these suggested addresses into geocoordinates.
A map tile server for the dynamic maps, preferrably one that is compatible with the default Leaflet map library.
A static map image server for the static map images e.g. on the proposal pages. This service is optional as Decidim will use the dynamic map tiles to generate a similar map element if the static map image cannot be provided.

One option is to host some or all of these services yourself as there are open source alternatives available for all of these services. More information about self hosting is available at the maps and geocoding configuration documentation.

You may also decide to disable some of the services that are not available at your service provider but in order to get the full out of Decidim, it is recommended to find a service provider with all these services.

In case you want to use different service providers for the different categories of map services, that is also possible. Instructions for this are provided in the maps and geocoding configuration documentation.

Creating your own map service provider

First thing you will need is to define a service provider module which also defines all the services your provider is able to serve. An example service provider module looks as follows:

module Decidim
  module Map
    module Provider
      module Geocoding
        autoload :YourProvider, "decidim/map/provider/geocoding/your_provider"
      end
      module Autocomplete
        autoload :YourProvider, "decidim/map/provider/autocomplete/your_provider"
      end
      module DynamicMap
        autoload :YourProvider, "decidim/map/provider/dynamic_map/your_provider"
      end
      module StaticMap
        autoload :YourProvider, "decidim/map/provider/static_map/your_provider"
      end
    end
  end
end

Please note that you will need to place the utility classes for each category of services under the paths defined for the autoloading functionality.

Defining the geocoding utility

For the geocoding functionality, Decidim uses the Geocoder gem which does most of the heavy lifting. It is not necessary to use this gem but in case your target service is already integrated with that gem, it makes this step much easier for you. Take a look at the list of supported geocoding APIs for the Geocoder gem.

In case your API is supported by the Geocoder gem, the only thing you need to do to create your geocoding utility is to create the following empty class:

module Decidim
  module Map
    module Provider
      module Geocoding
        class YourProvider < ::Decidim::Map::Geocoding
          # ... add your customizations here ...
        end
      end
    end
  end
end

If the target service has some other "lookup handle" defined in the Geocoder gem than :your_provider, you may want to override the handle method in the geocoding utility’s class you just defined. This is passed for the Geocoder gem as your lookup handle. An example of this can be seen in the Decidim::Map::Provider::Geocoding::Osm class which changes the handle to :nominatim instead of the default :osm which is not an existing lookup handle in the Geocoder gem.

In case you want to customize the geocoding utility for your provider, you can define the following methods in the utility class:

search(query, options = {}) - A common method for searching the geocoding API and returning an array of results. The results array contains the Geocoder gem’s result objects of type Geocoder::Result::Base or the result type specific to your API. If the first parameter is an address string, the method does a forward geocoding request finding the closest matching coordinate pairs for that address. If the first parameter is a coordinate pair array, the method does a reverse geocoding request finding the closest matching addresses for the search.
coordinates(address, options = {}) - A method that searches the best matching coordinates for the given address string. Only returns one coordinate pair as an array.
address(coordinates, options = {}) - A method that searches the best matching address for the given coordinate pair array. Only returns one address as a string.

Customization may be needed if you are not happy with the default results returned by the Geocoder gem. For instance, in some occasions you might want to pass extra query options to the geocoding API or sort the results differently than what was returned by the API and what is already done in Decidim by default.

In order to provide configuration options for the Geocoder gem’s lookup, you can pass them directly through the maps configuration with the following syntax:

config.maps = {
  provider: :your_provider,
  api_key: Rails.application.secrets.maps[:api_key],
  geocoding: { extra_option: "value", another_option: "value" }
}

This would equal to configuring the Geocoder gem with the following code:

Geocoder.configure(
  your_provider: {
    api_key: Rails.application.secrets.maps[:api_key],
    extra_option: "value",
    another_option: "value"
  }
)

Each geocoding API may require their own configuration options. Please refer to the Geocoder gem’s supported geocoding APIs documentation to find out the available options for your API.

Defining the geocoding autocompletion maps utility

For the geocoding autocompletion map functionality, you should preferrably use a service provider that is compatible with Photon which is already integrated with Decidim.

If this is not possible, you can also create a custom geocoding autocompletion maps utility for your own service provider by defining the following empty class to start with:

module Decidim
  module Map
    module Provider
      module Autocomplete
        class YourProvider < ::Decidim::Map::Autocomplete
          # ... add your customizations here ...
        end
      end
    end
  end
end

In case you want to customize the geocoding autocompletion map utility for your provider, you can define the following methods in the utility class:

builder_class - Returns a class for the geocoding autocompletion builder that is used to create the input fields for the autocompleted addresses in the front-end. By default, this would be Decidim::Map::Provider::Autocomplete::YourProvider::Builder or if that is not defined, defaults to Decidim::Map::Autocomplete::Builder. See below for further notes about the builder class.
builder_options - A method that prepares the options for the builder instance that is used to create the maps in the front-end. By default, this is an empty hash that needs to be configured for each provider.

To see an example how to customize the static map utility, take a look at the HERE Maps geocoding autocomletion utility.

In order to provide configuration options for the geocoding autocompletion, you can pass them directly through the maps configuration with the following syntax:

config.maps = {
  provider: :your_provider,
  api_key: Rails.application.secrets.maps[:api_key],
  autocomplete: {
    url: "https://photon.example.org/api/"
  }
}

And then you can use these options in your provider utility as follows e.g. in the builder_options method:

def builder_options
  { url: configuration.fetch(:url, nil) }.compact
end

You will also need to define a builder class inside your provider utility class as follows:

module Decidim
  module Map
    module Provider
      module Autocomplete
        class Here < ::Decidim::Map::Autocomplete
          # ... other customizations go gere ...

          # This is the actual builder customization where you could define e.g.
          # the JavaScript asset which is used to initialize the geocoding
          # autocompletion functionality in the front-end:
          class Builder < Decidim::Map::Autocomplete::Builder
            def append_assets
              template.append_stylesheet_pack_tag("decidim/geocoding/provider/your_provider")
              template.append_javascript_pack_tag("decidim/geocoding/provider/your_provider")
            end
          end
        end
      end
    end
  end
end

To see an example of the front-end JavaScript code that handles the geocoding requests, you can take a look at the HERE Maps example. You will have to listen to the geocoder-suggest.decidim JavaScript event on all elements that have the data-decidim-geocoding attribute defined which contains all the configurations returned by the builder’s builder_options method as mentioned above. For example, if you passed the following configuration from that method:

{ url: "https://photon.example.org/api/", other_config: "foo" }

This would be available in the JavaScript as follows:

$(document).on("ready", () => {
  $("[data-decidim-geocoding]").each((_i, el) => {
    console.log($(el).data("decidim-geocoding"));
    // => This would print out:
    // {url: "https://photon.example.org/api/", otherConfig: "foo"}
  });
});

When you hook into the geocoder-suggest.decidim event on these methods, the event callback will be provided three arguments:

event - The event that you hooked into
query - The text to be queried, i.e. what the user entered into the input
callback - A callback method which you will need to call with your geocoding autocompletion results once the request to the API has finished in the front-end.

The callback method expects one argument which is the array of result objects. The result objects need to contain the following keys:

key - The key which will be matched against the user entered input
value - The value which will be added to the address input if the user decides to select this value

Optionally, you can also include a coordinates key in the result object which contains an array of two cordinates (latitude and longitude respectively). You can also include any other data you might need in the front-end for these results but it will be not used by Decidim.

The final code would look something like follows:

$(document).on("ready", () => {
  $("[data-decidim-geocoding]").each((_i, el) => {
    const $input = $(el);
    const config = $input.data("decidim-geocoding");

    $input.on("geocoder-suggest.decidim", (event, query, callback) => {
        currentSuggestionQuery = setTimeout(() => {
          $.ajax({
            method: "GET",
            url: config.url,
            data: { apiKey: config.apiKey },
            dataType: "json"
          }).done((resp) => {
            if (resp.suggestions) {
              return callback(resp.suggestions.map((item) => {
                return {
                  key: item.label,
                  value: item.label,
                  coordinates: [item.latitude, item.longitude],
                  yourExtraData: item.yourExtraData
                }
              }));
            }
            return null;
          });
    });
  });
});

If your autocompletion API does not provide the coordinates information along with the autocompletion requests, you can hook into another event to do extra queries for the geocoordinates as follows:

$(document).on("ready", () => {
  $("geocoder-suggest-select.decidim", (ev, selectedItem) => {
    console.log(selectedItem);
    // => This would print out what you returned for the `callback` as shown
    // above.

    // NOTE: YOU DO NOT NEED THIS IF YOUR RESPONSE OBJECTS ALREADY CONTAINED THE
    //       COORDINATES IN THE `coordinates` KEY OF EACH RESULT OBJECT!
    // Then, once you know the coordinates, you trigger the following event on
    // the same input (obviously, you need to query the API first):
    const coordinates = [1.123, 2.234];
    $(ev.target).trigger("geocoder-suggest-coordinates.decidim", [coordinates]);
  });
});

Finally, if you want to pass these coordinates to the same form where your address field is located at, you can use the Decidim.attachGeocoding() method as follows:

$(document).ready(function() {
  Decidim.attachGeocoding($("#your_address_input"));
});

Now the latitude and longitude coordinates would be passed to the same form where the address input is located at. For example, if the address input had the name record[address], new hidden fields would be now generated for the geocoding autocomplete suggestion’s coordinates with the following names:

record[latitude] for the latitude coordinate
record[longitude] for the longitude coordinate

Then, you can read these values along with the form’s POST data in order to store the coordinates for your records in the back-end. This is not 100% necessary but it improves the accuracy of the geocoding functionality and it also avoids unnecessary double requests to the geocoding API (front-end + back-end).

Defining the dynamic maps utility

For the dynamic map functionality, you should primarily use a service provider that is compatible with the Leaflet library that ships with Decidim. You can also integrate to services that are not compatible with Leaflet but it will cause you more work and is not covered by this guide.

Please note that you do not necessarily even need to create your own dynamic maps utility if your service provider is already compatible with the Decidim::Map::Provider::DynamicMap::Osm provider. In order to configure your custom OSM compatible service provider take a look at the maps and geocoding configuration documentation.

If your service provider is not fully compatible with the default OSM provider, you can start writing your customizations by creating an empty dynamic map provider utility with the following code:

module Decidim
  module Map
    module Provider
      module DynamicMap
        class YourProvider < ::Decidim::Map::DynamicMap
          # ... add your customizations here ...
        end
      end
    end
  end
end

In case you want to customize the dynamic map utility for your provider, you can define the following methods in the utility class:

builder_class - Returns a class for the dynamic map builder that is used to create the maps in the front-end. By default, this would be Decidim::Map::Provider::DynamicMap::YourProvider::Builder or if that is not defined, defaults to Decidim::Map::DynamicMap::Builder. See below for further notes about the builder class.
builder_options - A method that prepares the options for the builder instance that is used to create the maps in the front-end. By default, this prepares the tile layer configurations for the Leaflet map.

In addition, you may want to customize the Builder class in case you are not happy with the default dynamic map builder functionality. To see an example how to customize the builder, take a look at the HERE Maps builder class. Please note that the custom dynamic map builder needs to extend the Decidim::Map::DynamicMap::Builder class as you can also see from the HERE Maps example.

The builder class works directly with the view layer and can refer to the view in question or any methods available for the view using the template object inside the builder. You may be already familiar with a similar builder concept if you have ever used the Rails Form Builder.

In order to provide configuration options for the dynamic maps, you can pass them directly through the maps configuration with the following syntax:

config.maps = {
  provider: :your_provider,
  api_key: Rails.application.secrets.maps[:api_key],
  dynamic: {
    tile_layer: {
      url: "https://tiles.example.org/{z}/{x}/{y}.png?key={apiKey}&{foo}&style={style}",
      api_key: true,
      foo: "bar=baz",
      style: "bright-style",
      attribution: %{
        <a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap</a> contributors
      }.strip
    }
  }
}

This will cause the following options to be available for the builder instance by default:

{
  tile_layer: {
    url: "https://tiles.example.org/{z}/{x}/{y}.png?key={apiKey}&{foo}&style={style}",
    configuration: {
      api_key: Rails.application.secrets.maps[:api_key],
      foo: "bar=baz",
      style: "bright",
      attribution: %{
        <a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap</a> contributors
      }.strip
    }
  }
}

And by default, this will cause the Leaflet tile layer to be configured as follows:

L.tileLayer(
  "https://tiles.example.org/{z}/{x}/{y}.png?key={apiKey}&{foo}&style={style}",
  {
    apiKey: "your_secret_key",
    foo: "bar=baz",
    style: "bright",
    attribution: '<a href="https://www.openstreetmap.org/copyright" target="_blank">&copy; OpenStreetMap</a> contributors'
  }
).addTo(map);

Defining the static maps utility

For the static map functionality, you should preferrably use a service provider that is compatible with osm-static-maps which is already integrated with Decidim.

If this is not possible, you can also create a custom static maps utility for your own service provider by defining the following empty class to start with:

module Decidim
  module Map
    module Provider
      module StaticMap
        class YourProvider < ::Decidim::Map::StaticMap
          # ... add your customizations here ...
        end
      end
    end
  end
end

If you want to use dynamic map elements for the static maps as well, you can leave the static map utility empty as shown above. Decidim will create a dynamic map replacement for the static map image in case the static map utility will not return a proper map URL.

In case you want to customize the static map utility for your provider, you can define the following methods in the utility class:

link(latitude:, longitude:, options: {}) - Returns a link for the given geographic location where the static map image is linked to. By default, this will return a link to www.openstreetmap.org.
url(latitude:, longitude:, options: {}) - Returns a URL for loading the static map image from the service provider. By default, this will return a link to the configured static map URL with the following URL query parameters:
- latitude - The value for the latitude option provided for the method.
- longitude - The value for the longitude option provided for the method.
- zoom - The value for key :zoom in the options hash (default: 15).
- width - The value for key :width in the options hash (default: 300).
- height - The value for key :height in the options hash (default: 300).
url_params(latitude:, longitude:, options: {}) - Returns a hash of prepared URL parameters for the url method. For the default parameters, see the explanations above for the url method.
image_data(latitude:, longitude:, options: {}) - Does a request to the URL defined by the url method and returns the raw binary data in the response body of that request. This data will be cached by Decidim once fetched from the API to speed up further displays of the same static map.

To see an example how to customize the static map utility, take a look at the HERE Maps static map utility.

In order to provide configuration options for the static maps, you can pass them directly through the maps configuration with the following syntax:

config.maps = {
  provider: :your_provider,
  api_key: Rails.application.secrets.maps[:api_key],
  static: {
    url: "https://staticmap.example.org/",
    foo: "bar",
    style: "bright"
  }
}

And then you can use these options in your provider utility as follows e.g. in the url_params method:

def url_params(latitude:, longitude:, options: {})
  super.merge(
    style: configuration.fetch(:style, "dark"),
    foo: configuration.fetch(:foo, "baz")
  )
end

When calling the url method with the latitude of 1.123 and longitude of 2.456, the utility would now generate the following URL with these configurations and customizations:

https://staticmap.example.org/?latitude=1.123&longitude=2.456&zoom=15&width=300&height=300&style=bright&foo=bar

If you want to use the dynamic map replacements for the static map images, do not configure static section for your maps:

config.maps = {
  provider: :your_provider,
  api_key: Rails.application.secrets.maps[:api_key]
  # static: { ... } # LEAVE THIS OUT
}

Even if you decide to use the dynamic map replacements, you will still need to define the static map utility because it is used to generate the link where users will be pointed at when they click the map image. In this case, the static map utility can be empty as you will not need any customization for it to work.

Configuring your own map service provider

After you have finished all the steps shown above, you will need to configure your service provider for Decidim. The configuration key for the example service provider referred to in this documentation would be :your_provider. For configuration, refer to the maps and geocoding configuration documentation.