I think they are referring to the level of detail/accuracy of the analysis - not just populations are examined, but analysis goes all the way down to the level of the individual plant.
"survey focused on individuals" would mean something different in my opinion, namely that the individual plant was the most important issue in the study.

Danke! Wäre "survey of plant positions" besser?

Moin!
Ich denke mit "survey of individual plant positions" bist Du ganz auf der richtigen Seite..