Description of the issue

This issue is part of the overarching issue #1510, the restructuring of quantities and quantity values.
We already have area value as a quantity, but it relates to two-dimensional spatial region. That does not seem correct, because the area value expresses the size of a two-dimensional spatial region. So area value needs to be a quantity value of size. Therefore we should implement size.

Ideas of solution

• area value

  • add the alternative label area quantity value.
  • add axiom: quantity value of some size
  • add axiom: is about some two-dimensional spatial region

• size
  - implement as a quantity
  - in VIM, there is not a specific definition of size, but a lot of ontologies use the one of PATO "A morphology quality inhering in a bearer by virtue of the bearer's physical magnitude." or AFO "Size is a quality quantification facet that quantifies the spatial extend of an entity." --> We could use them as an orientation and formulate the definition like: Size is a quantity that quantifies the spatial extend/physical magnitude of an entity.
  - quantities like 'length' (height, etc.) seem to be subclasses of size, which may be an important relation for further restructuring. For example, hub height could be moved, so that it is a subclass of size.