So if you are memorizing 5 min dates event, you would need not 100 cities, but 1000s of cities to memorize. It doesn’t seem practical.
But if it’s just some specific year that you intend to memorize seems quite good way. I am also thinking if it’s just for specific years. so 2001-2026 can also be represented by Alphabets A-Z (A could be Amsterdam, B could be Berlin and so on…)