Atlases

A USGS topographic map usually is named for the most prominent feature within the bounds of the map, which is frequently a community.
A plastic map is made with a water-resistant and tear-resistant type material, but it retains the flexibility and other characteristics of paper maps. 
Proposals to change the name of a natural feature may be submitted to the U.S. Board on Geographic Names as described below. However, there must be a compelling reason.
Yes, GNIS actively seeks names of features that no longer exist. There are more than 100,000 such entries in the database now. To search for them, type the word "(historical)" (along with other name words if desired) in the name field.
The GNIS contains named communities, both incorporated and unincorporated, but these communities do not necessarily correspond to ZIP Code areas. ZIP Codes are unofficial entities developed and maintained by the U.S.
There are no official definitions for generic terms as applied to geographic features. Such definitions as exist derive from the particular needs and applications of organizations using them.