Was Vivec really bigger than the Imperial City?
It was a lot bigger. It had like fifteen cantons or something, and each canton had a top level, a middle level, a lower level, and a canolworks level. Each level (with the exception of the canolworks) had interiors for shops and things. It was so large that there was a fast travel gondola system just for the city itself.
And yeah, I always got lost in Vivec too. =D Luckily the NPCs are actually helpful when you ask for directions, unlike Oblivion NPCs. I asked a guard where the shops were in the Imperial City, and he gave me a full list of what shops there were, and told me they were in the Market District. Where is the Market District? Find it yourself.