Brendan,

May I ask what you mean by "AMS" maps in your U.S. topo collection?  Looking at your Maryland set (my state), you indicate that purple is for maps from both AMS (1:25,000) and USGS (1:24,000).  I work with the map collection at the University of Maryland library - we have almost all the USGS 1:24000 maps for the entire U.S., but only a few state collections (most incomplete) of the 1:25000 maps.  Both the 24K and 25K maps were produced by the USGS.  We have sets of "AMS" maps, but they were Army Map Service maps mainly of countries in Europe, Africa, Asia, etc. I believe our library received those AMS maps (mainly older maps from the 1930s-50s) because we are a depository library entitled to receive publications from the U.S. Government, and those older Europe, etc., maps were 'left overs' from the World War II era?  Thanks!

Jim Nealis

Map Volunteer, Univ. of Maryland McKeldin Library