Symbol and layout representations can be found in various areas, including BIM. (See also Section 5.12.11, “Classify Electrical Parts ”.)
Both layout and symbol representation describe abstractions of the physical 3D model. They differ both in regard to the level of abstraction and in regard to the focus conceptually. When layouts focus on the geometrical 2D representation of the physical model, symbol representations focus on the logical functionality of the model. Both concepts are not interchangeable.
Layout: According to ISO 5455:1979, layouts have in particular the property of scale, i.e. the scaling factor between the 2D graphic and the 3D model. In particular, this means that you can define sizes such as height and width for layouts that are directly linked to the 3D model.
Symbol representation: The symbol representation as a logical description of the functionality of the part represents a deeper abstraction of the physical model, in which all properties such as height, width and depth, insofar as they relate to the 3D model, are omitted. Only the circuit diagram symbol is shown.
We can illustrate this difference in a simplified way using two transformers: One transformer feeds an overhead line, the other is used to charge the cell phone. If the scale remains the same, the layout representations of this situation are very different, reflecting the different physical dimensions of these two transformers. In both cases, the symbol representation can remain the same. In the CNS classification, layouts are described by the class CNSCAX|GFX|LAYOUT and (logical) symbol representations by CNSCAX|GFX|SYMREP.