(5000m² rice paddy)
Today’s a busy day, so I chose an easy place name.
It’s made of 3 kanji: 五 go (five), 反 tan an obsolete unit of area (used for land, cloth, etc…), and 田 ta (rice paddy).
1 反田 = about 1000m² or roughly 1/10th of a hectare.
Therefore 5 反田 = about ½ a hectare.
As it was just a bunch of rice paddies that compromised a subdivision of 大崎村 Ōsaki Mura (Ōsaki Village), the area was relatively insignificant until 1911 (Meiji 44) when a Yamanote Line station was built here. (By the way, the next station is Ōsaki).
As a place name, it’s not unique. It also occurs as a family name.
And there are other numerological variations.
一反田 Ittanda (1)
壹反田 Ittanda (1)
二反田 Nitanda (2)
三反田 Santanda (3)
八反田 Hattanda (8)
千代反田 Chiyotanda (1000)
An interesting note is that without a numerological prefix, the surname 反田 is read as Sorita, not Tanda.
As for Gotanda, I have nothing really to add to this except that there is a famous yakuza “family” based in the area, and as such there a lot of sex shops and a few love hotels operating there. It’s not all grimy, though. The area is a popular drinking town because (1) it’s on the Yamanote Line and (2) there are many sex shops there. Oh wait…