The principal shopping area in Istanbul is, undoubtedly, the Grand Bazaar, with more than 4,000 shops crammed beneath its roof.
The Grand Bazaar is the largest shopping area in all of Istanbul. 
mnli hypothesis: The Grand Bazaar is the largest shopping area in all of Istanbul.  premise: The principal shopping area in Istanbul is, undoubtedly, the Grand Bazaar, with more than 4,000 shops crammed beneath its roof.