US Postal Department Post Route Maps

I recently ran across various state and regional maps on ebay that were printed annually it appears that list each post office, DPO's, RPO route, HPO routes, etc. I was interested in an Illinois map from 1958. I am unsure of value and scarcity of these paper maps. They seem to range in price from $9.99 upto $75 depending on when they were printed, condition, and state/region. I think they would look great framed and helpful in research. Has anyone else any info regarding post route maps?

I haven't studied it much, but you might find this link to a 2011 USPS Publication to be interesting reading:

http://about.usps.com/publications/pub119.pdf

Thanks I've printed it out and will check it out.

To give everyone an example of what I am rambling on about...

Here is the item number for one of the maps found on ebay: 160659358594

Here is a direct link:
http://www.ebay.com/itm/Post-Route-...em25680b4382