We already saw the layer declarations for some different types of underlying data. A WebGIS application is usually tasked with working with multiple layers, so having a layer manager of some sort seems to be a reasonable requirement. We're not going to be getting into details about how this has been achieved as it is simply down to showing a couple of checkboxes that turn layers on/off. Also, the source code is available so you can check it out easily. Our manager is a static one - it does not allow layer reordering. After all, our application is meant to be rather simple.