- The cafe is located on the backside of that building
- You will find the ph no on the backside of the book
- You have to search for it on the backside of the shelf
So on and so forth...
In many of the cities in India that I have lived in or travelled to, I have heard the usage of 'backside' in a similar fashion but not as commonly as in Mumbai.
Even though am no expert in the language, I doubt that the usage is incorrect but it's informal meaning is so commonly known & used that one would hesitate to refer to buildings, books, roads etc as having 'backsides' (i.e. instead of back entrances or behind...).
back·side: noun 1.the rear or back part or view of an object, person, scene, etc.; that part which is opposite the front. 2. (informal) rump; buttocks. (source: www.dictionary.com)
Whatever the reason might be, it does seem that 'backside' has caught the fancy of the locals and is here to stay... offering many amused moments to those who first stumble upon it.