I read a map of Imperial City (Oblivion) on this website I found, and I was wondering if the cities in Oblivion were bigger and more highly populated than Skyrim. On the map it seemed like there was much more stuff in the city.

I have no exact numbers at hand but I think that the cities were a bit bigger in size but less NPCs. Solitude however seems like a Cyrodiil city since it's big and you barely see any people outside

The Imperial city is far bigger with a much higher population than anything seen in skyrim. As for the rest of the cities in oblivion, i would say they are significantly bigger than all of the cities in skyrim but with much less detail.

i use to get lost all the time in Imperial City seemed huge to me

It was. There are 195 citizens (excluding guards) in the Imperial city alone, as opposed to Skyrim's most populated city, Solitude, with only 79 people (excluding guards and the few generic dockworkers).

Citations: (http://www.uesp.net/wiki/Oblivion:The_Imperial_City) (http://www.uesp.net/wiki/Skyrim:Solitude)

In my opinion, I'd rather have less people and more content though.

The Imperial City was more populated than any of Skyrim's cities, but it was essentially six cities with doors between them. The majority of Oblivion's other cities were smaller in population than Skyrim's however, and almost all of Skyrim's NPCs haves few lines of unique dialogue.

To be honest, the IC (Imperial City) felt like the only authentic city in Oblivion.

With that in mind, the cities of Skyrim all feel similar to the cities of Oblivion that were not the IC.

I guess I just imagine cities being huge with so many NPCs that you cannot remember who is who and where they are.