Well here is what I found after a quick search
http://www.piercelaw.edu/tfield/copyvis.htm
Copyright arises automatically once an original effort has been started and some aspect of it has been fixed in a tangible medium (including those for use with computers). One need not even have notice on published copies. Registration is required only if legal action is warranted. However, giving notice and promptly registering works provide important remedial advantages in the U.S.
Copyright does not give an owner the right to sell or distribute a work. For example,
consider one person's drawing of another's painting. Even if copyrightable (and it may not be),
the drawing would infringe copyright in the original painting.
As discussed earlier, copyright gives its owner the exclusive right, for example, to reproduce protected subject matter (such things as ideas and facts being excluded). Sometimes a question arises as to whether a second, similar work was copied or independently created.
If the person creating a second work had access to the original work and the works are virtually identical, copying is likely to be presumed even if the chance of access is remote.
http://www.the-artists.org/exh/art-copyright.cfm
When does copyright apply to a work of art?
As soon as an artist creates a work of art, it is protected by copyright. Artists (or their agents) then have the right to determine how and when a work can be reproduced. Although copyright laws vary from country to country, generally the duration of copyright is 70-75 years after the death of the artist. After this time, the work is no longer under copyright and can be reproduced without additional clearance or fees. Any artwork created by a living artist or an artist deceased fewer than 70 years may be subject to copyright.
As such, the artist or their representative must be contacted for copyright clearance and they are entitled to royalties.
SO based on this stuff RJbeals, your map has been stolen (as far as I see it). The new artist had copies of your works and plainly said he use them to make his own. And they basically look the same. I am not sure if you have any desire to pursue legal action but I think yo umight have a case.
WM