"All pots and pans should be flat on the bottom for heat conduction and smooth on the bottom to not cause scratching. Many glass cooktop manufacturers include instructions saying not to use cast iron cookware, but modern cast iron, without the "raised ring" on the bottom will work fine. The cookware bottom should be smooth so as not to scratch. Move anything across the glass top cookware or otherwise by lifting rather than scooting. Lastly, if a pot or pan is heavy which any can be if it is full of food take care not to drop it on the glass cooktop. All these rules apply whether the cookware is aluminum, cast iron, or stainless steel."
from the
Cookware Manufacturers Association's website.
Ian