From what I can see, today's civilian national flags are all rectangular, with the sole exception of Nepal.
For the sake of uniformisation, and according to the type of flag required, they will fit either a 2:3 (small flags) or a 3:4 ratio, except for Qatar which seems to like flowing in the wind.
The "official" flag, meaning the first version adopted and documented as national colors, is usually not used except perhaps in official documents or in letterheads or in other printed forms (eg. stickers) or also on square banners.
(eg. as often carried by the Swiss guards at the Vatican)
The Royal Palace in Brussels sports a 3:4 flag, not the original 28:32 version.
Monaco is red up, Poland is red under.
The red thing might be the flag of the Republic of Flight in the States, in Africa it is a preservative for elephants.
Vimanav, I knew it was not from a bicycle...
but still a wheel