"Five large cities, comparatively larger than those in Oblivion, are available to explore (and to be attacked from above by dragons)..." http://www.uesp.net/wiki/Skyrim:Skyrim
Yet I have read through several topics claiming that the cities are in cells once again (and yes I am lazy to research this myself). The devs have stated that these dragon attacks are not scripted, but if cities are in cells how can this work? Do dragons have the ability to enter cells? And if that is the case what will happen if we leave the city/cell with a dragon inside - will it come out for us or will it be an easy way to escape?
Could it be that there is a certain probability that a dragon will spawn in the city cell and attack? I hope not!