I think the most important part about the abstraction process is that we have to ensure that the most clinching characteristic that makes it identifiable quickly remains in the pictogram.
Also, I think that a pictogram may mean different things when used in a different context. I.e. a pictogram of a person cycling placed by a pathway may mean that the pathway is meant for cyclists to use. On the other hand, the same pictogram may mean "beware of cyclists passingby" if placed by a zebra crossing. So, question of "to whom" it is for is also important here.
Since there are also plenty of ways to represent an idea, I think it'll be useful to know which prototype best describes the idea in a way that is most intuitive for the viewers.