Cartographers and Printmakers, Georg Brain and Franz Hogenberg, co-authors of Civitates Orbis Terrarum produced remarkably detailed and accurate cityscapes of nearly every major city in Europe and many in Asia and North Africa as well, what sources did they use in the making of this atlas?
I find hard to believe that they both could have visited every they made likenesses of, to me at least it seems likely there must have been earlier maps or writings they consulted.