I just listened to an episode of 99 PERCENT INVISIBLE about flag design and I wanted to take a stab at it. I took a few minutes and made this flag for my city, Altoona, Iowa.
North American Vexillological Association principles of flag design
1. Keep it simple
2. Use meaningful symbolism
3. Use two to three basic colors
4. No lettering or seals of any kind.
5. Be distinctive
I tried to follow these principles however I don't have time to research so I am not sure how distinctive it is. Blue and green have already been used in Altoona's branding, but I chose some more exciting hues. The blue in mine somewhat represents the river to the west of us that runs through Des Moines. The green can also represent the farmland in the area. The middle triangle can be a capital A for Altoona and an arrow pointing positively to the future.