Here[0], we see two separate cards next to each other, with the same dimension, but at a different elevation. As a result, one casts a larger shadow.
Here[1], they specify that "Shadows are never approximated using material". Wouldn't that require that one of those two cards with the same dimension appear to be larger, since it is closer to the eye?
What do they mean by that rule?
[0]: https://www.google.com/design/spec/what-is-material/objects-...
[1]: https://www.google.com/design/spec/what-is-material/material...