I'm guessing the authors here are referring to the fact that many places were really poorly drawn. There was high detail in regions where the map makers were local to but this got fuzzy real fast. Some would even do things like plant fake cities on their map as a means of fraud detection. A secret signature if you will. Someone who copied their map was likely to copy the fake place.

You're definitely right that this has a lot to do with early mathematics but remember that that is a small part of map making. How do you define coast lines? Rivers? Borders? The devil is in the details. With older maps the general shapes would be (usually) accurate but it could get fuzzy around the edges. Literally. It's not like they could get a picture from space, or even from the sky. It would take years to measure many things that would take us minutes now