The Beginner's Guide to OpenLayers 2.10 says the following:
This property determines if the map should behave as a Mercator-projected map. Setting this to true will allow us to use other layers, such as Vector layer, with the actual map projection.
Given that there is already a method where the projection is specified, i.e. in
map.projection, why is there a need to specify the same thing over again in the
Layer property? Is there a situation where a different projection is required in Layer as compared to the map?
Or do they serve totally different purpose?