Reading or studying Buddhist, Hindu or Tantric literature, two often encountered expressions are Cremation Ground and Graveyard Meditations. Considering that both are complete misnomers, it would be desirable to create better terms - yet seeing that they are abundantly used in literature, we can better choose the approach of forming a mental image fitting the reality and then attach that new concept to the existing terms.
Fact is, in most instances when the above terms are used, there are neither any graves to be found nor has a cremation occured. What is meant, and for which there simply is no term other than Charnel Ground, is an area covered with human bones, half or whole skeletons, more or less putrefying corpses and disattached limbs; among which wander growling dogs as well as crows, ravens and vultures - exactly the stuff that (Western) nightmares are made off. And exactly for that very reason, such locations were/are utilized in order to confront one's fears and to realize the transient nature of life.
Here, amidst this vision of their own and everyone's future, yogins and yoginis, Shaiva Kapalikas and Aghoris, shamans and sadhus walked, sat, chanted, exercised, meditated; sometimes staying and living among the dead for long periods of time.
Now everyone who has ever seen a cremation (in India or Nepal) knows that little is left unburned and what is, will be carried away by a river together with the ashes and perhaps some logs not fully burned down. Also, everyone who has seen a graveyard, of whatever confession, knows that there rarely are open graves nor do bones or skulls stick out of the ground.
So the images invoked by the words graveyard or cremation ground are misleading and essentially wrong. What we're dealing with is a much more ancient form of corpse disposal, one practiced not only in Tibet or old India (before cremation became common), but among tribal peoples in South East Asia as well as among the Zoroastrians of Persia: giving the corpse back to nature (who acts in the form of animals and the elements).
In the Tibetan case, Westerners have started to call this custom a sky burial; though again, there is no burial (from "to bury") involved at all. Rather, as the Tibetan word jhator ("giving alms to the birds") clearly shows, it is a form of exposing the corpse to nature.
To contemporary, Western sensitivities, and if one is not used to such treatment of death since childhood, the idea seem "terrible" - but such an emotional judgment is indeed an acquired one and rather "local" when viewed on a global scale and within the historical time-line of humanity.
With the above in mind, i.e. a "field of death", a "valley of corpses" or a charnel ground, one can also more easily understand where the wandering sadhus and tantric yoginis found/find the supplies for their so-called Charnel Ground Ornaments and Implements; items made from human skulls or bones.
It is good to keep this in mind when the next time you encounter the term Shmashana (Skt., smasana), which is most often translated as "cremation ground", sometimes as "graveyard".