The discussion is here:

https://groups.google.com/forum/#!msg/re3-dev/b-Yue9L9Zso/NC0rJMqc2YwJ

```
3. The map directive has a "gaTopicChange" listener that calls 
gaLayers.loadForTopic (which sends a request to the layers service). 
````

We wouldn't need gaLayers in this directive then.