Shown to wander in the outskirts of Preston (6)
I believe the answer is:
proven
'shown' is the definition.
(thesaurus)
'wander in the outskirts of preston' is the wordplay.
'wander' becomes 'rove' ('rove' can be a synonym of 'wander').
'in the' is an insertion indicator.
'outskirts of' suggests removing the centre.
'preston' with its centre taken out is 'pn'.
'rove' going into 'pn' is 'PROVEN'.
'to' is the link.
(Other definitions for proven that I've seen before include "Established with evidence" , "Conclusively demonstrated by evidence" , "Established beyond doubt" , "Adjective meaning demonstrated beyond doubt" .)