I have created an SCCM 2012 Visio overview. This after searching high and low, and even asking Microsoft for a Visio diagram, and my searches ending in zero.
The SCCM 2012 Visio just shows a cookie cut / low level overview. This is by no means a solution for every organization. The diagram involves different hierarchy options. Not all sites will have a CAS, two primaries, or even secondary sites.
You can either save the SCCM 2012 Visio JPG for you consumption or click below to download the SCCM 2012 Visio PDF version.