The reposition phase in my current game is going to be rather massive on scale, as I intend to abandon and resettle close to 400 towns. Actually, I may abandon every town without a wonder.
Normally during the conquest phase, I raze anything wonderless and have settlers follow my armies and lay out my cities then. But, my current game didn't have a conquest phase...
My repositioning will likely take hours, but the funny thing is that it will only take a single turn. Everything will be railed and irrigated by then, and I don't plan to do until I've constructed Longevity, so they should grow fast once settled.