It's just a basic skirt shape with some lines marked. Years ago I cut something like this out of paper using a string for a compass, and it’s come in handy dozens of times, for all kinds of applications.
So I thought I'd share.
Here it is in printable pdf so you can use it, too.
This single piece can make a simple A-line skirt with a gentle flare, either gathered with elastic or with a waistband or yoke. Measure how long you want the skirt to be and use the appropriate cutting line.