The Spanish made several attempts to colonize the area north of Florida, none of which went particularly well for them. The Ajacan Mission was one of their smaller attempts, consisting of only a handful of missionaries, a servant boy, and a Native guide that had been abducted as a young man ten years earlier.

The Mission lasted only from September 1570 to February 1571. Their Native guide, who had been baptized as Don Luis, had abandoned the missionaries and returned to his own people. Two of the missionaries went to bring him back and were killed, after which the Ajacan Mission was attacked and all but a servant boy working for the missionaries were killed. The boy lived with the Don Luis' people for a while before eventually being returned to the Spanish when someone eventually came to check up on the missionaries.

The exact location of the Ajacan Mission remains unknown, so the map you have is probably just estimating a probable location. It was likely in the vicinity of Paspahegh or Chiskiack (map), which are the two communities which Don Luis is hypothesized to have come from and where he returned to. You'll also see some speculation that Don Luis is the same person known to the English colonists later in history as Opechancanough, who became the leader of the Powhatan Confederacy after "Chief Powhatan" died, but I haven't found the arguments for that connection compelling yet.