First, to nest, you need 2 maps. call one router map and the other switch map.
on the router map, you'd have the router object and the object SWITCH MAP (actually use the map as the object mapping to).
On the switch map, you would have the object switch itself.
Second, when you nest maps, the system has to update all nested objects as well as top map objects to ensure the status is correct for all objects...this is what allows issues to propagate up to top maps from nested ones. I ran into huge issues upgrading to 9.5 and had to break out my maps into smaller ones and put in frames so the updated at different times and would propagate fairly quickly.
Hope that clarifies and makes sense
So im clear then basically. I would have the geography map with perhaps the routers and then a switch map just the switches and nest them together???
We have a top level jpeg describing our major sites and I have dragged individual map icons on each site. Each of these site maps only has the site's local topology drawn. In busy sites, I additionally have up to 6 sub maps which describe, for example, the WAN links, the user distribution or the server distribution. Be careful to simplify these maps so that when an element goes red, it will reflect up through the tree correctly and allow you to quickly drill back down, without any duplication or confusion. The "use an element only once" rule is only for your convenience. You can actually use them as many times as you like.
The actual process could be to create your first empty site maps, or whatever you want, and then drag these icons onto your top level map, placing them on an appropriate jpeg in an appropriate way. Then go back through each of the site maps and drag that site's elements onto it.
The simpler each map is, the quicker they will paint up on the browser.