All the content of your map is organized into layers.  The layers button displays the layers screen which is where you go to turn layers on and off, browse the contents of a layer, or change how a layer is configured.

Base Layers
The base layers section lets you choose the type of backdrop for your map.  You can select one of the following:

Auto Select
When this option is selected, the map will display the "Roads" backdrop when you are zoomed out and automatically switch to the "Aerial Photography" backdrop when you are zoomed in.

Aerial Photography
The background aerial photography is provided by Google Maps.  Google calls this "satellite" view but for most populated places in the United States this is high resolution ortho photography taken from aircraft.  

The Roads view displays roads and other landmarks.

This view displays a shaded relief map with some course contour lines.

Not a very interesting backdrop but it has its uses.  Use this backdrop if you want to print out just your Map Layers with no background.  Also, the map will automatically change to this backdrop when you want to zoom in closer that the other base layers allow.

Map Layers
The map layers section lists all the layers that you have added to your map either by drawing or importing.  You can turn these layers on and off in any combination using the checkboxes.  
Layer is turned off
Layer is turned on
Layer is turned on but you need to zoom in closer to see it.  See 'Min Zoom' on the settings screen.

Click on the layer name to browse the layer, search the layer, setup the layer, or more.  All of these layers are viewable by all users on your account according to permissions setup for the account.  

Add A New Layer
Click this link to add a new layer to your map.  See the Create New Layer topic for more information.  Any layers you add will be viewable by all users on your account.  Only users setup as managers of a map can add and remove layers from that map.  Another way to create a new layer is to import an existing layer.

Layer Order
If you are the map manager you can change the order of your layers by clicking the up/down arrows to the right of any layer name.  This will prompt you to indicate the new position you wish to move this layer to.  For example, enter 0 to move the layer to the top of the list.

Video on this Topic
See Video:  Basic Features of Diamond Maps