This technique layers an illusion over a location, causing it to look like a different location. Because of how wide an area the illusion can be placed over, that in turn makes it easy to trick others: any who enter the area will be affected by the illusion and see the false location. But to create an illusion on such a large scale and to potentially deceive so many people raises the chances that the trick will be discovered by someone who is familiar with genjutsu.
in: