Luke knew clearly that only by working together could they find the treasure, so he didn't want to conceal anything but rather wanted to gauge their attitude, and said, "There are two ways.
The first way is to find ancient navigation maps that are both old and detailed. Back then, the island's terrain where the treasure is hidden likely hadn't changed, allowing us to locate the treasure island by matching geographical positions.
The second way, if the island's terrain has changed, it's likely because vegetation has been destroyed, leading to soil erosion and some low areas being submerged by seawater.
But the central area of the island is often higher and won't be affected. We can compare the higher terrain areas of the treasure island."
