Complex sentence: South 24 Parganas is an important district of West-Bengal.With urban fringe of the metropolitan city of Calcutta on one side and the remote riverine villages in the Sundarbans.
Split into simpler sentences: South 24 Parganas is an important district of of West Bengal. I would seem to be within the urban fringe of the metropolitan city of Calcutta on one side and the remote riverine villages in the Sundarbans.