And a big part of the design strategy for the app is to retain that simplicity.

FORBES: Move up http://i.forbesimg.com t Move down

It is also notable for the harmonious relationship between the open and built spaces, the simplicity of its design, and its size.

UNESCO: Culture

We know certain images can become iconic through simplicity of design, openness to interpretation and relative ease of reproduction - the Apple logo for example.

BBC: Too famous to see?