It does not give any information about the dept of the equipments or valves. The pneumatic and electrical signals are shown as dashed and dotted lines. The transfer of materials from one equipment to another equipment is shown as a solid line. The interconnection between them is shown as a line. In PID, the equipments and the process control instruments are represented as two dimensional symbols.
They are also commonly referred to as isos in process and chemical industries and in academics also. A piping isometric drawing is also a detailed diagram which is used to represent pipes, pipe fittings, bends, valves, welds etc.
