Design process consists of multiple coherent stages in which a lot of factors involve and their impact on each other is inseparable. Design is a process of transfer, translates, and interact the concepts and internal ideas of designer through sketches. Visual reasoning is the main factor in connecting designer's knowledge and experiences through sketch and continues till achieving a satisfactory result. This is a systematic way of using sketches to set up a new sub-goal that can then trigger a reasoning process through mediating sketches. Sketch is a vital part of conceptual design stage of a new production. Sketch has a special set of attributes that help the human mind in translating descriptive propositional information into depictive information. Sketch can be the key factor in stimulating and improving design creativity. Developing creativity and old ideas, reinterpreting ideas, simplifying idea retrieval and old information that emerge to simplify different visual ideas, are among the usage of sketch. The process of graphic representation can be defined as a conversation with oneself, in which we can communicate with sketch. This communication process is in relation with the image drawn on a paper, eye, brain and hand. In addition to making temporary decisions, sketch enables us to evaluate and interpret a design analysis without omitting other options. It has been shown that sketch illustrates how we think of problems, not what we think of them and therefore it is very important. Sketch produces knowledge and on the other hand knowledge is revealed via sketch. This shows the interrelation between design knowledge and sketch. It is more obvious that sketch describes objects faster than writing and it is a stimuli and linking tool that develops a relationship and interaction between all of the ideas and mentality. Illustration is a special crisis for a creative designer. He/she should depend on a plenteous collection of visual memory. The affluence of this collection depends on active and extended visual perception. Using sketch notebook is an appropriate way of collecting visual language and accurate observations, as it gives priority to seeing rather than watching. The importance of drawing in design process is that each signing action is an external depiction of part of the information. Most of design sketches enable the designer to have flexible thinking in different contexts. Creative designers expand their skill in effective free-hand sketches and use them while thinking. The designer uses sketch to think about current functions and revising them and find new spatial relationships and edits old spatial relationships. Conceptual sketches are produced fast, not only to adjust designer's primary ideas, but also is an effort to understand and introduce the problem. Free-hand sketches facilitate lateral transfers (movement from one idea to another with a little difference) and prevents early fixation and helps solving problems and extracting ideas. The purpose of this research is to evaluate the key role of sketch in design process and also suggest a proper method for reforming the efficiency of design process regarding the advantages of sketch.
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