The following image shows the impact of a 1 megaton nuclear explosion on San Diego.
Estimated fatalities: 278,040
Estimated injuries: 541,960
Click the map for a larger image.
An interactive map for this city is available here.
Here’s a simplified description of the blast zones that result from a nuclear detonation. A more detailed description is available on the NukeMap website.
Fireball: Yellow zone at very center of display. Everything in this zone is vaporized.
Moderate Blast Damage: Next zone from center, colored gray. Most residential buildings collapse, injuries are universal, fatalities are widespread.
Thermal Radiation: Next zone from center, colored yellow. Third degree burns extend throughout the layers of skin, which can cause severe scarring or disablement, and can require amputation.
Light Blast Damage: Largest zone, colored gray. Windows can be expected to break, causing many injuries in a surrounding population who comes to a window after seeing the flash of a nuclear explosion.
Here’s a video which describes the impact of a nuclear explosion on a city.