Like many cartographers of his day, Delisle did not travel with the explorers. He drew maps mostly in his office, relying on a variety of data. The quality of his maps depended on a solid network to provide him first-hand information. Given his family's and his own reputation, Delisle had access to fairly recent accounts of travellers who were returning from the New World, which gave him an advantage over his competitors. Being a member of the "Académie", he also kept current with recent discoveries, especially in astronomy and measurement. When he could not confirm the accuracy of a source, he would indicate it clearly on his maps. For instance, his "Carte de la Louisiane" shows a river that the baron of Lahontan claimed he discovered. As no one else could validate it, Delisle noted a warning to the viewer that it might not exist.