One has schemes about lowlands (6)
I believe the answer is:
plains
'lowlands' is the definition.
(thesaurus)
'one has schemes about' is the wordplay.
'one has' becomes 'i' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'schemes' becomes 'plans' (I've seen this before).
'about' is an insertion indicator.
'i' placed inside 'plans' is 'PLAINS'.
Can you help me to learn more?
(Other definitions for plains that I've seen before include "Large areas of level country" , "Flats" , "Grasslands" , "Flat tracts of land" , "Prairies" .)