When A Nuking Is Preferable...
CarlosLabs have an interesting Google Maps toy. Enter the name of your closest city, choose from a variety of kilotons for a nuking, hit the nuke it button, and find out whether you'd die from vaporisation, flaming flesh or radiation cancer.
Here's what survives around Sydney after a 340kiloton nuking :
This is damage impact zone if a (Dinosaur age ending) asteroid smashed into Australia, with Sydney as ground zero :