If it is filled in with soil, then crops are likely to grow better than the surrounding plants, making a spot of larger, greener plants, as seen in image 2.
By studying the landscape, particularly vegetation, it is possible to locate potential grave sites. Crop marks are a case in point. Take a hole in the ground. If it is filled in with soil, then crops are likely to grow better than the surrounding plants, making a spot of larger, greener plants, as seen in image 2.