Complex sentence: Bridgeton, Millville and Vineland are the three principal cities of the Vineland-Millville-Bridgeton Primary Metropolitan Statistical Area, which encompasses those cities and all of Cumberland County for statistical purposes.
Split into simpler sentences: Bridgeton, Millville and Vineland are the three principal cities of the Vineland-Millville-Bridgeton Primary Metropolitan Statistical Area. It encompasses those cities and all of Cumberland County for statistical purposes.