In the Force Awakens, Han says that Luke disappeared to find the first temple. I assume that's what he and Leia were told, or assumed themselves. However in the Last Jedi, Luke says he went there to die.
The map isn't a map to Luke's location, it's a map to the Jedi Temple on Ahch-To, its location uncovered with the assistance of Jedi scholar Lor San Tekka. When Luke's disappearance becomes known to the Resistance, they send Poe to contact Lor and he gives them a copy of the same map that Luke has been using on the assumption that that's where he's gone.
WHEN IMPERIAL FORCES surrendered in the aftermath of the Battle of Jakku, Luke Skywalker began a lengthy quest to recover as much lost Jedi knowledge as possible. Over the years, he uncovered tantalising clues as to the origin point of the Jedi, but its exact location remained a mystery. When he finally did piece together its location with the help of the old scholar Lor San Tekka, Skywalker kept this information to himself. An unnamed island, located in the northern latitudes of Ahch-To, was the site of the first Jedi temple. It was this world, and its temple island, where Luke would eventually hide away from the galaxy.