Diagram is the process of abstracting and simplifying an idea so that it can be easily understood. It is a record of physical and spatial features that define the unique and distinctive features of a building, site or program. One of the reasons we do diagrams for that arch. drawings can be hard for the public and clients to understand, so we use diagrams to explain the most important parts of the "concept" using simple drawings that everyone can get easily. And by removing all the other details that can make the concept harder to see, the public can see your idea clearly.