Copies of the cloth maps can be found:
Computer-generated maps of Sosaria can be found:
The Ultima 1 Character Statistics page at Ultima Thule! has a list of sign posts and the bonuses they imbue on visitors. Additionally, this site's Ultima 1 Economy pages provide lists of shops where you can buy anything from weapons to transportation.
The Ultima 1 technical file by Plaid Dragon, on the Ultima Online Archive, gives all the details of every place on each continent.
There is a list of interesting places that is on the Complete Guide to Ultima 1, part of Prescient Dragon's Hint Network.
There is excellent information about places on the Ultima I Shrine on the RPG Classics Shrines. The principle behind the generation of dungeons is explained; the overworld is shown with tiled maps and marked with locations; the sign posts are listed with their locations and effects; space is explained in detail and towns are explained excellently.