Inspired by this question, in order to estimate the damage that would have been caused had Ultron's plan succeeded (or indeed would/should have been caused even though it failed) it is necessary to make a guess as to just how big Sovokia city, or the chunk of it lifted into the air, actually was.
The relative ease of evacuation suggests that it was rather small, perhaps only a kilometer or less across, but is there more direct evidence? (Perhaps some of the long shots show individual buildings that are also shown closer up?)
How big was Sokovia city?