What is it with “larger than life” questions?
Generally, “Symbo”l is a figure that is used to transmit a message and represents in an understandable manner, independently of any language, an object, concept or state.
Generally, “Legend” is a caption, title, or brief description.
Small notes like “SEE SEPARATE PARTS LIST” or “CONFIDENTIAL” are considered legends.
Also, “legend” can be used to identify the “symbols”. In this case legend is often called “key”
The need in the legend / key arises when non-standard symbols, or symbols from many different standards are used, like in construction drawings where drafting, electrical, plumbing, meteorological, etc. symbols may be used all together.
So, the purpose is to keep the drawing unambiguous.
If you show examples of drawings that give you hard time, we could possibly be of better help.
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