I hope this may help...
- General Arrangement drawings are used mainly in Project / Process Engineering, to show, and locate equipment respect to the co-ordinate system within the plant or field, showing only those dimensions, datum, elevations to refer each equipment to other equipment or structures. Is common practice to indicate (in plan wiew) a short description (type, capacity, power,...). A valve is referred into the pipeline showing it basic specifications( diameter/type/standard), distance from pump, height from floor, and special connection specifications. This valve will be identified by a TAG number or code.
- General Assembly drawings, show the equipment referred to itself, and is used mainly for location, anchoring, connections, maintenance. In some complex equipment there may have several disciplines or sub-assemblies (electrical, control, pneumatic...)General Assembly drawings are more usual in Design Engineering, ad usually are provided from equipmet manufacturers. General Assembly drawings uses the PART NUMBER.
I work from 15 years in Conveying Design Project Engineering. When I start... I had many fights to define this and other topics.
¡ Best regards to all from Chile !