RATP - Régie autonome des transports parisiens - the autonomous association of Parisian transport - is the company that operates the metro and other public transport in Paris
RER - Réseau Express Régional - train network serving Paris and the suburbs
Translation of the text on the cover: RATP - RER - Line D Path 1 and 2 Inter-station “Gare du Nord - Châtelet” Dry column supply connection "Poissonniere"