The yoko in Yokohama (横浜) has only short vowels.
The woman’s name Yōko has a long ō:
Yōko (洋子: ocean + child)
Incidentally, the kanji for 洋子 break apart in an interesting way. One might think that Yōko is the child (子）of a wet 
sheep (羊)!
But Yōko Ono (or more precisely, Ono Yōko) is generally rendered in katakana:
オノ・ヨーコ Ono Yōko
And what about the kanji for Ono? It’s 小野 (small + field).
So if Ono is 小野 (small + field), ….
and if Obama is 小浜 (small + beach), ….
maybe Yoko Ono and Barack Obama need to get together in some way!
No disrespect to Michelle Obama intended, of course!
