A primarily big survey on land is not concrete (8)
I believe the answer is:
abstract
'not concrete' is the definition.
('abstract' is the opposite to 'concrete')
'a primarily big survey on land' is the wordplay.
'primarily' says to take the initial letters.
'on' says to put letters next to each other.
'land' becomes 'tract' (I've seen this in other clues).
The first letters of 'big survey' is 'bs'.
'a'+'bs'+'tract'='ABSTRACT'
'is' is the link.
(Other definitions for abstract that I've seen before include "Academic" , "Extract; summary" , "Intangible" , "sculpture by Hepworth" , "a work of modern art" .)