What you see here is a side by side comparison of Nerima as it is depicted in the manga and an actual photograph of Nerima. As you can see, they are pretty similar. The actual photo shows the large storm drain that is frequently shown throughout the manga.
This is Shakujii Koen (Shakujii Park) an actual park in the Nerima area of Tokyo. In the manga, it is never referred to by name, but the large lake and rowboats are what gives it away. On the right is the park in reality.
On the left is the fictional Springs of Jusenkyo where the characters recieved their curses. On the right is the actual area where Jusenkyo is said to exsist, Bayankala Mountain Range in the Qinghai Province of China.
This is a typical high school in the Nerima area. As you can see, it looks a bit like Furinkan High School. But for the record, many Japanese schools share this similar layout.
The resembalance between the money hungry Tendo sister and Louise Brooks is uncanny, especially in this side-by-side comparison. Louise Brooks (1906-1985) was a famous movie star of the silent era. Here career didn't last past the 1930s, but she's become something of an icon of the Roaring Twenties.
Takahashi was obviously inspired by this Leyendecker painting from the 1920s. Leyendecker was primarly known for his painted advertisements for the Arrow Collars and Shirts company. Apologies for the quality of the painting, as it was taken from a postage stamp.
The costume designs for the Romeo and Juliet themed episode were taken from the 1968 Romeo and Juliet film directed by Franco Zeffirelli. The film starred Olivia Hussy and Leonard Whiting. This is considered by many to be the best film adaptation of of the classic play.