Updated Use Cases (markdown)

Use-Cases.md

@@ -34,6 +34,10 @@ var map = new ol.Map({
 
 This alternative can be implemented if the layer knows the map projection.  The vector layer is responsible for calling `source.protocol.read({success: callback})` where the callback calls `source.parser.parseFeatures(data, {projection: projection})` (`data` is supplied to the callback and `projection` comes from the map's view).  The layer maintains a cache of features in the map view's projection, and these are supplied on demand to layer's the renderer.
 
+_Questions from Eric:_
+
+Why does the layer need to know about the map/view projection for implementing this? The layer renderer knows about the map/view projection, so it can be the one providing the projection.
+
 ### Generate features in app and add to a layer
 
 User writes an application that generates features at run time.  These features are added to the layer for display and interaction (e.g. popup on selection).