The Gordon Bennett Memorial is a fascinating task. It relies on pilots dropping a physical mark near a target, but they are limited in what that area may be. 

This shape can be anything defined by the director. The shape is typically made on white paper, similar to the fabric of the target. In the example to the left a mark at the top of the ribbon would be the best result, but a mark outside of the ribbon would be invalid for scoring in spite of being a better result.

This task can be difficult from an organizers perspective because it requires much more time and effort from the measuring team because of the fabric required to set the shape. As a result, a common variation is using pre-existing shapes such as roads and driveways. This requires the establishment of how much of the marker must be in to be in (typically phrased as "any weighted portion". 

Gordon Bennetts are often used as memorial tasks because of the flexibility allowed, typically using the shapes of a key characteristic of a person. 

If you are looking for an interesting read, look into the Wikipedia page for Gordon Bennett himself.