1. A projection system including multiple projection apparatuses, the projection system comprising: a first projection unit configured to project a first pattern image on a first projection area; a second projection unit configured to project a second pattern image on a second projection area, the second projection area partially overlapping the first projection area; and a first image capturing unit configured to, when the first pattern image is projected on the first projection area, perform first image capture to obtain a first captured image by capturing an image capture area including the first projection area and at least a portion of a second projection area and, when the second pattern image is projected on the second projection area, perform second image capture to obtain a second captured image by capturing the image capture area, wherein the first projection unit projects a first partial projection-target image extracted from a projection target image based on the first captured image, the second captured image, and the projection target image on the first projection area, and the second projection unit projects a second partial projection-target image extracted from the projection target image based on the first captured image, the second captured image, and the projection target image on the second projection area.