Factual error: When trying to contact Tahiti control, the pilot mentioned that their position is close to JENNA, which is an IFR waypoint. This waypoint can also be seen on the plane's navigation display. The problem is, JENNA is in Louisiana and nowhere close to the Pacific Ocean.
Continuity mistake: At the Christmas meal, Chuck gets passed the candied yams. When he takes the yams, there is a spoon in the dish. When the shot changes to behind him, the spoon is not in his hand. (00:14:30)
Factual error: When Chuck cleans out the pocket of the dead pilot, we see the pilot's employee ID badge. He is employee number 186801 and was hired in 1987. I was hired in 1992 with an ID number of 161XXX. My brother was hired in 1988 with an ID number of 88XXX. The pilot's ID number should have been lower than my brother's.
Other mistake: When Tom Hanks throws the spear at the fish it's sticking straight up. He's too close for that to happen. He would've had to throw it straight up a long way for that to happen.
Answer: Cast Away was filmed on an island called Monuriki. It's part of a group of islands called the Mamanuca Islands, in Fiji.