atlas vs reference book

atlas and reference book both are nouns.

Word	Noun	Adjective	Verb	Adverb
atlas	Yes	No	No	No
reference book	Yes	No	No	No

As nouns, reference book is a hypernym of atlas; that is, reference book is a word with a broader meaning than atlas:

Other hypernyms of atlas include book of facts, reference, reference work.

atlas (noun)	reference book (noun)
a figure of a man used as a supporting column	a book to which you can refer for authoritative facts
the 1st cervical vertebra
a collection of maps in book form