I overlaid the 2000ft. and 1000ft. radius of blast over Hamburg (3rd picture) and it doesn´t even cover the old, 14th century area ofthe city (yellow line), not to speak of ww2 area. All of Hamburg is build from structures comparable to those of Hieroshima, which remained standing. A nuke would just reassemble the debris caused by the various conventional bombing raids that city was subject to. It would -in my opinion- not have the power to wipe out large cities as long as the building structure was NOT WOODEN. Nagasaki and Hiroshima are not very large cities.
Please note also the image taken from Hieroshima at ground zero: The area destruction effect caused by blast and heat effects is remarkable and frightening but The concrete buildings do not show much damage, as a matter of fact, they remain standing (1st picture).
I overlaid historic photographs of Nagasaki before after the bomb with the current google earth picture (see below, 2nd picure). Note that the destructive force reduces greatly at a distance to point zero: At 1000ft. distance, bridges remained standing, at 1500 ft. distance, large factory buildings (no. 17) were heavy damaged but not destroyed.
It would require a nuke with a figure of merit of 60 to 80 compared to that dropped over Nagasaki to wipe out Hamburg.