Understanding type sizes, line lengths, and line spacing

- What size is this type font?…Well, I can tell you,…it's 48 points.…That's what the computer says.…How would you know that if the computer didn't say so?…Can you put a ruler on it and tell that it's 48 points?…That would be great, but you can't.…There's no way to know the size of a type font…by looking at it and measuring it,…and this can be frustrating.…It's commonly thought that the point size of a type font…is from its tallest ascender to its lowest descender.…

Sounds logical, but it's not the case.…A characters point size is not the height…of the character itself, but of the invisible…bounding box that contains it.…Here's the thing, the character can be any size…that fits in the box,…which you can see looking at Park Avenue.…Same sized box, much smaller type.…This goes back to the days of letter press,…and hot metal type, when characters would be cast…on metal slugs.…

Very similar to those old typewriter keys.…Typically the designer, or punch cutter,…would leave a small space top and bottom…so letter parts wouldn't get lopped off during printing.…