There was a question asked here about using cast iron on glass top ranges. In the responses, there was a link to an article about cast iron equipment. Here is a quote.
There is also an almost comically simple alternative for a more permanent fix. It's one of those ideas like the safety pin or the paper clip: blindingly obvious in hindsight, but not apparent at once. Just sandpaper the pan or pot bottom smooth! Readers have reported to us that they have done just that, with excellent results. We don't have details, but we'd guess that two grades of sandpaper, a coarse then a fine for polishing off, would do the job.
I am getting my first brand-new electric glass-top range, and I don't want to ruin it. The quote said they are guessing, but with Stack Exchange, there is no guessing just real experiences. How do you polish the cast iron to make the bottom smoother? Did you see an improvement?