Is Adlatum an official continent of the Dragonlance world or just a fan project?
Well, both. Adlatum has been mentioned in two of Tasslehoff’s Map Pouches as a place located northwest of Ansalon. There is also a very brief mention in the Dragons of Krynn sourcebook by Margaret Weis Productions. As far as Adlatum being officially recognized as a continent, that has never been directly stated in official Dragonlance continuity. However its status as a continent can be easily inferred from the Dragons of Krynn reference since it is mentioned along with Taladas and Ansalon. Regardless of what Adlatum is, the content of the Adlatum setting–with the exception of its location and the information given in the Dragons of Krynn reference–is entirely unofficial and has been put together as an “unofficial” fan-made project. Of course, there is nothing from WotC that says that what we put down in the PDF sourcebook and the Nexus isn’t official.
