Desired length to heel?

Hi. I have a question and I may have trouble explaining exactly what I’m asking, so let me know if it’s unclear. I’m working my first sock pattern, and I don’t like socks that are extremely tall. I know how high I want it to go on my leg (I want it to be a “quarter” sock, if you know what I mean by that) and I’m supposed to work the pattern the desired length to the heel, then do the heel flap. The problem is, I don’t know what the structure of a heel flap is, and so I don’t know how much to work before I do the flap. Like, am I supposed to measure how high the sock should be all the way to the floor and work that much, then do the heel? Or should it be from how high the sock should be to the ankle bone, or what?

Does the question make sense? Can you please explain how much of the top of the sock I should work before my heel flap?

I’ve always taken it to mean how much you want in pattern until you start the stockinette for the heel at the back of the foot, I guess around the bottom of your ankle bone.

Thanks! I just didn’t know how high the “heel flap” starts above the very bottom of my foot. Thanks for the quick reply!