Calling Back: An Example for Google’s Geocoder Service and Custom Markers

I recently moved and naturally there was a lot of clothes which I do not need (read: do not fit in) any more. Throwing them away would be a waste and luckily, there is a social business called WAMS which (besides a lot of other nice projects) supports reuse and recycling. WAMS provides and maintains containers for collecting clothes on many locations in Tirol. Unfortunately, there is not yet a map available to find them easily. I took this as an opportunity for a little side project in Javascript. I am not affiliated with WAMS, but of course the code and data is open sourced here.


The idea was quite simple. I used some of the container addresses I found in the flyer and created a custom Google Map showing the locations of the containers. The final result looks like this and a live demo can be found at the Github page.


Retrieve Geolocation Information

The Google API allows to retrieve latitude and longitude data from any given address. If the address was found in Google’s database, the Server returns a GeocoderResult object containing the geometry information about the found object. This GeocoderGeometry contains the latitude and longitude data of the address. The first step retrieves the data from Google’s API by using the Geocoder class. To do so, the following JSON structure is iterated and the addresses are being fed to the Geocoding service.

The Javascript code for obtaining the data is shown in the following listing:

As the calls to the Google Services asynchronously, we need to use callbacks which are called when the function before has finished. Callbacks can be tricky and are a bit of a challenge to understand the first time. Especially the Google Geocoder methods require to work with several callbacks, which is often referred to as callback hell. The code above does the following things:

  1. Iterate over the JSON structure process each container individually -> function processContainers()
  2. For each container, call Google’s Geocoder and resolve the address to a location -> geocodeAddress(container, processContainerLocationCallback)
  3. After the result has been obtained, process the result. -> processContainerLocationCallback(container,lat,long)
  4. Update the JSON object by looping over all records and search for the correct id. Once the id was found, update latitude and longitude information. -> updateJSON(container,lat,long,printJSONCallback)
  5. Write the result to the Web page -> printJSONCallback()

The missing latitude and longitude values are retrieved and the JSON gets updated. The final result looks like this:

Now that we have the data ready, we can proceed with the second step.

Placing the Markers

I artistically created a custom marker image which we will use to indicate the location of a clothes container from WAMS.

wamsThis image replaces the Google standard marker. Now all that is left is that we iterate over the updated JSON object, which now contains also the latitude and longitude data and place a marker for each container. Note that hovering over the image displays the address of the container on the Map.

Hosting the Result

Github offers a great feature for hosting simple static Web pages. All is needed is a new orphan branch of your project, which is named gh-pages, as described here. This branch serves as the Web directory for all your files and allows to host Web pages for public projects for free. You can see the result of the project above here.


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