How did Harker research his destination?

Harker researched his final destination by visitong the British Museum where he utilized the book and maps they had available on Transylvania.

Having had some time at my disposal when in London, I had visited the British Museum, and made search among the books and maps in the library regarding Transylvania; it had struck me that some foreknowledge of the country could hardly fail to have some importance in dealing with a nobleman of that country.