Here are some of my theories about skyrim, would like to hear your opinions
1. Nirn is a small world, like a lot smaller then Earth, some evidence for this is:
arrows fly straight and don't fall much until they hit something, lower gravity of small world wold explain that.
you can carry up to 400 pounds of equipment, that is twice your body mass, again lower gravity
you can fall from great heights and survive
dragons can fly even tough their wings are too small for the body
giant spiders can walk, in our world they would collapse under their weight, no way their legs could support them
the same with giants
this coupled with disasters like oblivion crisis, the war and various dangers like bandits and monsters could explain the low population of Skyrim.
2. Whiterun is in fact a castle, not a city, its layout is more consistent with a castle and it is small enough to be one
the layout of york castle is rather similar in layout to Whiterun. the 4 cities are Winterhold, Riften, Solitude and Markarth, the other four are larger villages.