3 suggestions

I recently downloaded a freeciv java client.  I have a few suggestions that
might be useful.

(1)  For the map view, it might be worth you looking at the map view
component I wrote for the project I work on - the java client for freerails.
The projects still in the early stages of development, but there is a
working map view component.  See:
http://sourceforge.net/projects/freerails/
(Let me know if you would like more details.)

The next two are not really that important, but should be easy to fix.

(2)  I find having to set the datadir a bit of a pain.  Have you considered
using className.getResource() instead, which allows you to load resources
relative to the classpath among other things?

(3)  In jdk 1.4 'assert' is a reserve word.  Maybe it would be a good idea
to replace 'assert(' with 'assertThat(' to avoid a lot of warning messages
when compiling under 1.4.

regards

Luke