New Utility: Ultima Mapper
Fenyx, who manages the Codex of Ultima Wisdom wiki, has released a utility on Github for viewing maps of the dungeons in Ultima 4:
Tool made for the The Codex of Ultima Wisdom for displaying dungeons
Files from Ultima games are not included in this repository. You will need to place *.DNG files, CHARSET.EGA and WORLD.MAP from PC version of Ultima 4 in the Maps directory.