Suppose an author is intending to create a book using several (unmodified, pre-arranged/ordered) illustrations which are available under a CC BY-SA 4.0 license. Is the author required to share the entire book as CC BY-SA, or can the author license the book (or text) in any desired way, provided the images are clearly still under CC BY-SA and properly attributed. Phrased differently, I'm unsure if the book as a whole constitutes an adapted material from the illustrations.
The CC BY-SA 4.0 legal text defines such adapted material as follows (emphasis added):
Adapted Material means material subject to Copyright and Similar Rights that is derived from or based upon the Licensed Material and in which the Licensed Material is translated, altered, arranged, transformed, or otherwise modified in a manner requiring permission under the Copyright and Similar Rights held by the Licensor.
It appears to me that the book is based upon the Licensed Material (the illustrations), but they are not altered, transformed, modified etc. so this would not constitute an adapted material.
Is this understanding correct? Intuitively this would be saying that the share-alike clause only applies to work which modifies, alters etc. the illustrations themselves, but not for works which simply use the illustrations. I'm unsure about that, but mainly suspicious of this interpretation since I'm not sure I'd have reached the same conclusion for the legal text of CC BY-SA 3.0.
For the record, the illustrations do form an important part of the book, and the author would not be claiming to use the images under fair use, nor am I convinced the book would count as a collection (although, unless I've misunderstood, which is very possible, collections aren't an exception to the share-alike clause of the CC BY-SA 4.0 license, only prior versions).