I came across a link to something called "The Literature Map" this morning. It's interesting because you can enter in the name of an author you like, it does a fast search, and then it matches other authors with the name you entered.
In other words, if you love James Patterson, when you enter his name a group of other authors will come up that are supposedly the kind of authors that people who like James Patterson will read. Fans of James Patterson read, X, Y, Z authors, too.
But I'm not sure how accurate or up to date it is. I'm not even sure who runs the site. I read James Patterson and was surprised to see Lee Child came up. I don't read Lee Child and probably never will. It's just not my thing. And I wasn't too fond of the other authors that came up with James Patterson either.
And is it up to date? I don't know. I do know that when I typed in the names of my favorite genre and sub-genre authors I couldn't find anything. Clearly, it's not like doing an amazon search. And I know these authors are people with good sales and tons of publishing credits...not to mention readers.
If you are so inclined, check the site out for fun and find out for yourselves. Maybe I'm way off base. But I have a feeling this might be, allegedly, more of a promotional tool than anything else.