Hope the title wasn't misleading.
So I was studying text faces and display faces for a face I want to design, theorizing about xheights and things like that, when suddenly... see attached.
(I know you'd never set large blocks of text in a bold, but bold makes this illustration more clear.)
I'm wondering about vertical metrics. What I wish to understand is, what makes Parkinson a display font that you'd never use for blocks of text, and what makes Whitman such an awesome text font? Also, more fundamentally, I wish to understand what the hell point size has to do with the actual vertical metrics of typefaces?
Parkinson Medium @72pt and Whitman (Roman or Bold) @88.5pt have damn-near the same xheight and cap-height. @72dpi, the Parkinson @72pt measures 72px from desc-line to asc-line, while the Whitman @88.5pt measures 83px from desc-line to asc-line.
I know the answer is "that happens sometimes" (QED), but my hope is to understand what's happening.
IS there a true-ish statement that can be made along the lines of "Usually, about ____% of the time, in a good text face the cap-height is about ____% of the point size and the xheight is about ______% of that, and the ascenders and descenders do such-and-so..." ...?