Appearance of characters by river (7)
I believe the answer is:
texture
'appearance' is the definition.
'characters by river' is the wordplay.
'characters' becomes 'text'.
'by' means one lot of letters go next to another.
'river' becomes 'ure' (river in Yorkshire).
'text'+'ure'='TEXTURE'
'of' acts as a link.
(Other definitions for texture that I've seen before include "Quality or feel of material" , "The way a fabric, say, feels to the touch" , "Surface grain" , "Quality of material felt by touch" , "Quality of fabric" .)