There is a term for a corridor such as this; it is called a VERANDAH.
I have heard this term applied to houses and public buldings (museums/libraries) and I don't quite see why it can't be similarly used for the external walkways of apartments.
A verandah (I think it must have a Portuguese root; AnnaS might know more)is a long paved corridor running along the entire length of the front of the house/building. Akin to an extended front porch. It has a roof but is otherwise open to the elements; it also usually has a decorative balustrade or a parapet interrupted by columns which support the cantilevered roof. A fine example of one such is the commonly called 'front porch' of the New York Public Library.
Might we use this term for the exterior corridors of high-rises? Back at you, board! tsuwm?
[aside]My understanding of some of the terms used above:
A terrace is not always paved; it could even be a terraced garden. A patio is always paved.
A balcony is a smallish roofed patio, attached almost like an outgrowth, to the upper storeys of buildings (both apartments and multi storeyed houses). It is usually an extension of a bedroom or of the living room to the outside, and has access only from the 'inside' of the room.
