The original poster's question cannot be answered with any degree of certainty, before the 19th Century Burial Acts in England and then there may be other peculiarities, even after the Burial Acts?
If you want the exact answer, have the time to check if the answer survives and it is a Cemetery after the Burial Acts in England, you might find your answer (1800 to 1900) in Government files and correspondence, or in some Local Authority correspondence in County Archives or with the Council or County or Local Authority if a cemetery in their possession.
Also check the first Burial Book or Churchyard Book a notebook (sometimes called the Sexton's Book) if it survives (besides the Burial Register), or newspapers of when a 19th Century burial site opened, or when it was in its planning / development stage, because sometimes depths, water table depth (water table should be well below the deepest burial).
Also records of local Burial Boards.
Surviving plans (Sexton Plans) of the Grave layout of Cemeteries and a measuring survey of the Cemetery (assuming the original boundaries can still be determined and not been extended or reduced). Also part or all of the burial ground might be built over (which I feel should be banned), but measuring might give some idea, like buried near this spot.
Also look at, or near the base of surviving headstones, they might have a grave reference.
Look for Compartment Markers on Corners of a whole sectional area, sometimes where two paths once met or alongside paths, where they survive.
Also there may once have been paths through a 19th Century cemetery, where nobody was buried.
But a Grave Plan I have seen doesn't distinguish which burials were on top, or which were side by side grave burials!
A Husband and Wife may have purchased two Freehold graves, so that they can lie side by side (nobody on top), whereas some other Freehold graves will have burials on top.
Under some Headstones is a Vault (seen a brick chamber being built with Engineering / Blue bricks near my Son's grave), concrete beams are built in near the top and concrete panels fit into the beams (like a Bison Beam house floor), a concrete layer seals that, then soil and grass. These Vault graves with one headstone, can take up to two or more side by side burials and burials on top.
Some ancestors purchased a Freehold grave for two and only one was used. The Wife moved away and was found buried in another town. So nothing can be assumed.
BURIALS
http://discovery.nationalarchives.gov.uk/results/r?_ep=Burials&_cr=HO&_dss=range&_sd=1800&_ed=1900&_st=advBURIAL
http://discovery.nationalarchives.gov.uk/results/r?_ep=Burial&_cr=HO&_dss=range&_sd=1800&_ed=1900&_ro=any&_st=advBURIED
http://discovery.nationalarchives.gov.uk/results/r?_ep=Buried&_cr=HO&_dss=range&_sd=1800&_ed=1900&_ro=any&_st=advEXHUMATIONS
http://discovery.nationalarchives.gov.uk/results/r?_ep=Exhumations&_cr=HO&_dss=range&_sd=1800&_ed=1900&_ro=any&_st=advYou may find more under Cremation and other related words.
This is basically only a "HO" search via The National Archives website and other Government Departments took over from the Home Office and inherited records from the predecessor Department, so you might need to see their Departmental records too. See The National Archives Guide covering Burial Correspondence and Records held separately by Government, that went to the Public Record Office (P.R.O.) name changed to The National Archives.
Parish Churchyards were so overcrowded that they were digging up the bodies and bones of those previously buried and throwing them back in with the newly deceased and at one place people were seen carting the previously buried dead away in wheel barrows.
Goodness knows where some ended up
If you go into a parish churchyard in a flattish town surrounding the churchyard and need to go up steps from the current street pavement and the cemetery churchyard is level with, or near the top of the boundary wall, it is possible that the Churchyard has been built up by the addition of soil.
Sorry if this puts you off your breakfast, but the body matter was seeping out the bottom of churchyard boundary walls and onto the street, in some towns. Hence the need for the State to become involved and bring about the Burial Acts (someone else has mentioned).
I was also surprised that the floor levels in some churches have been changed too. You will likely know if the church floor has been relaid, if the floor memorial stones have some of the writing cut off.
It is no wonder that there was terrible disease in the local population and polluted water.
Later, you had to get Planning Permission for a Pig-sty, as some were too close to wells and drinking water was getting polluted.
Mark