Sort of clock face seen crossing grand city centre (7)
I believe the answer is:
digital
'sort of clock' is the definition.
(digital clock, as opposed to an analogue clock)
'face seen crossing grand city centre' is the wordplay.
'face' becomes 'dial' (dial is a kind of face).
'seen crossing' indicates putting letters inside (cross can mean to go around).
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'city centre' becomes 'it' (centre of the word 'city').
'g'+'it'='git'
'dial' enclosing 'git' is 'DIGITAL'.
(Other definitions for digital that I've seen before include "(Watch) without hands" , "Made up of numerals, a watch or other display" , "Showing data in numbers" , "form of technology" , "Of watch, showing time in numbers" .)