Tokyo used to be a smoker’s paradise, but there now are restrictions on smoking, particularly in public. Many wards of Tokyo have rules prohibiting smoking in public; these neighborhoods restrict public smoking to designated smoking areas called 喫煙所 (kitsuen-jo) or 喫煙エリア (kitsuen area).
Glossary:
喫煙所 (kitsuen-jo) = smoking area
公衆喫煙所 = public smoking area
公共喫煙所 = public smoking area
指定喫煙場所 = designated smoking area
区指定喫煙所 = ward-designated smoking area
無料喫煙所 = free smoking area
指定喫煙場所 = designated smoking area / smoking corner (uses the same kanji 喫 used in kissaten)
A smoker area in Shimbashi:

A smoking area near Shibuya crossing, visible on Google Maps:

A lovely smoking area along the Kanda River (near exit 5 of the Hibiya Line Akihabara Station).

Smoking areas in various Tokyo wards:
Taito-ku smoking area map (link):
Toshima-ku smoking areas (link)
Chiyoda-ku smoking areas (link)
Shibuya-ku smoking areas (link)
Chuo-ku smoking areas (link)
See also:
- Smoker’s map points way to safe havens (The Japan Times)