If you see a cat roaming around, first make sure that it doesn't belong to a neighbour. You can then contact CASCA (Comité d'Aide et de Secours pour les Chats Abandonnés) which is the only entity with the authority to decide whether or not a cat needs to be captured and put up for adoption.

DO NOT TRY TO CACTH A CAT before receiving the green light from CASCA.
CASCA is not an "actual place" or shelter for captured cats. CASCA will advise you of the best time to catch cats if they need to be spayed or neutered and what procedures to follow.

You can contact CASCA by email at adoption@cascaorg.com.