What mergers and sales have done to your favorite travel guidebook

When Penguin and Random House announced on October 29 that they would merge, a chill went through the guidebook industry. The two global giants are the last of the big six publishing houses -- soon to be a big four -- to operate travel series: Penguin has Dorling Kindersley's Eyewitness series and Rough Guides, Random has Fodor's, Knopf Guides, and National Geographic Travelers guides.

The Penguin family was already on poor footing as the publisher was in the process of deciding on Rough Guides' and DK's future following a 30-day review of the businesses. Now that Penguin and Random House are combining operations, what will become of each of its travel brands remains to be decided.

Outside of this new mega-publisher, the big houses have shed or shut down their travel series. Macmillan rid itself of Frommer's in 1999 and HarperCollins hasn't published an update to its Access series in four years. It's notable that when Frommer's was on the block from March to August of this year, the buyer that emerged was Google, not a book publisher.

The chart below shows the strength among the independents, as well as the role non-traditional publishers now play in the industry: The two largest guidebook brands in the U.S. are now owned by an arm of the BBC and by a search engine.