Like many readers, I was enraptured by the maps in J. R. R. Tolkien's The Lord of the Rings (1954-55) and The Hobbit (1937). After their 1965 reprinting in a widespread American edition, maps became more common in works of science fiction and fantasy. I particularly enjoyed the maps of an imaginary kingdom in Lloyd Alexander's Prydain Chronicles(1964-68) and star charts in Cherryh's Chanur series(1982-92).
I think it would be worthwhile to split this question into science fiction and fantasy genres, as these genres have often taken separate paths in literature. I am not sure whether to classify Jonathan Swift's Gulliver's Travels (1726) as science fiction or as fantasy. This is certainly an early example of speculative fiction illustrated with maps, but I would be more satisfied to find the earliest use of a map in the modern genre of science fiction that began in the 19th century with authors such as H. G. Wells and Jules Verne, as it might have influenced later authors.
To sum up: What was the earliest printed map in the modern science fiction genre? (That is, not merely the earliest map to be mentioned in a text.)