It's the origin of 99 Percent Invisible's name: https://99percentinvisible.org/

I was about to recommend an episode or two, but it's an institution at this point. If you have a reasoned opinion about flags, there's a reasonably good chance it's because you saw or heard Roman Mars talk about vexillology. https://www.ted.com/talks/roman_mars_why_city_flags_may_be_t...