Flag Stories is an online project that tells the visual story of flag design, and it’s pretty fascinating:
Sure, there are a lot of books and websites covering the different aspects of flags like history, demography and culture, through heavy text, but we wanted to add new aspects to this field by only looking at the graphics and telling the story visually. So we started this Flag Stories project to discover the hidden stories behind the graphics.
Basically we started looking at all the flags in the world and squeezed all the data we could possibly gather into a blank spreadsheet. The more we dug into it, the more stories we managed to reveal, so our plan is to keep digging and continuously adding new stories to the project. Wikipedia has been our most used source for information, but you will find the specific source list for each visual at the bottom of the page. We have included flags of the UN member states.
BONUS: See also this great TED Talk by Roman Mars of 99% Invisible on why US city flags are so badly designed.