I did some research about Map labeling and most of them are about font, spacing, etc.
I am just wondering is there any rule of thumb of labeling in terms of map scale.
For instance, in Google Maps map zoom level 3, Country Names and Ocean Names map zoom level 4, Big Cities and Seas ... and so forth.
I tried to do some search and somehow I couldn't find any.
Can you give me some advice or places where I can start to do research?