Many of the maps to be included are already online at the LoC website, but the new partnership will make them accessible in the same place as other collections, for example from the Smithsonian Libraries and the Internet Archive.
Many kinds of maps are useful for postal history research, and postal maps can be found in libraries around the world. For example, a search of the LoC’s online maps for “postal” yielded 27 results, including, for example, an 1871 railroad and post office map of Minnesota and Wisconsin.
Do you have a favorite source for maps? Leave a link in the comments!