'Backbone' L3 Map - map without end-device subnets
On dynamic L3 maps, normally you will see all subnets attached to a device, even if those subnets do not inter-connect to any other devices.
Usually, these subnets terminate end-devices, customers, etc.
If you want to see just a 'backbone' map of your network, you can clear these subnets from the map using a filter.
This filter will filter all subnets that only have 1 monitored device in them (usually this device is your router - the gateway for customers).
return ($object->type != 1) || (GetObjectChildren($object) != null);
The filter works by removing all subnets that have only 1 child object under them.