preliminary drawing or sketch
A drawing (sketch) or a plastic model, made to give an idea of an object, or its operation.
For comp refers to the graphical version, the preliminary draft of a work.
Need arises for the author and also to illustrate the general features of creation, the idea of making easy to understand and to study possible developments to be transferred to the finished product.
The sketch or draft assumes different names and meanings, as well as manufacturing techniques, depending on the type of work that is "sketches".
Often the sketch, the subsequent processing and evolution, are an integral part of the project and determine its main characteristics, then developed and refined in the final design and construction of the executives.
The sketch or sketch (sketch in English) is used in many fields of art and design.
In sculpture, the sketch is often used as a scale model of the final and is used to create and study the composition.
If a particular quality has value in itself, as a graphic work, demonstrating and communicating effectively with the spirit which moved the creative act and design.