Promising to be a complete walkthrough for ten games set in or around the world of Ultima, this is slightly misleading. After all, the book is only 320 pages, and surely there's a Hellsteed of a lot more going on, especially in the later games, than could be encapsulated by even the best team of editors and writers in so small an area.
Your suspicions are correct. There's a lot going on in the first few titles, and the guide devotes a mere few pages at best to the first two Ultima games (five pages for Ultima I, seven for Ultima II), along with Akalabeth, the precursor to the Ultima series. Ultima III is where the guide ramps up, with 21 pages worth of maps, gameplay tips, and charts. Fully half the book is given to Ultima VII and Ultima VIII content.
This book also comes with a double-sided, fold-out color poster which shows the overworld maps for all the games. This poster is bound in between pages 145 and 146, but sadly my copy of this is missing, so I wasn't able to include it (and I'm not sure I have the skills necessary to stitch together a giant poster from multiple image files in any case). All apologies.
Update: user @Xuio has graciously provided a high resolution scan of both sides of this poster map for us. You can download it here: