The first group are itineraries included in the Red de Interés General del Estado (Spanish highways network), which generally either serve as long-distance connectors beyond the Catalonia's field or either have a special strategical importance.
The second group are itineraries mainly used for Catalonia's internal transport.
However, some of these highways (such as C-31, C-32 or C-58) are main communication paths and suffer from heavy traffic.
The category field indicates if the sections are autopistas (generally tolled freeways under a concession contract), autovías or simple single-lane roads.
The primary highways managed by the Catalan Government serve mainly for transport inside Catalonia.