A "--" in the district column means, that the town is a district-free town, i.e. it is by itself a district.
... (Austria) 1976 - Niki Lauda, (Austria) 1977 - Jody Scheckter, (South Africa) 1978 - Patrick Depailler[?], (France) 1979 - Jody Scheckter, (South Africa) 1980 - ...