Question arose during an rpg session, as you can probably guess.
I've found some information on graveyards in Venice, but nothing conclusive as to what, exactly, did they do with dead bodies in, say, Renaissance. The Republic was predominantly Catholic and logically it would follow the Catholic funeral rites, but wasn't land scarce enough to warrant some other arrangement, such as cremation? And wouldn't the bodies put in damp soil be a huge health hazard?
To the best of my knowledge (forgive me, my area is textiles of the region, and my knowledge of forensic anthropology hasn't wandered into Venice yet) Venice used crypts beneath churches to house the corporeal remains of the dead. I know there has been an ongoing issue with rising water levels in these churches and their crypts, and attempting to preserve them.
I know that in the 16th century San Pietro di Castello was the cathedral church for the region, but was mostly overshadowed by San Marco. I know San Pietro has large underfloor burials, and San Marco has HUGE crypts (multi story deep). San Zaccaria has very large (and beautiful) crypts.
Now, the advantage of such crypts at least is that they require much less storage space for bones than full burials do. So there is that.
See also Ruskin, The Stones of Venice: The foundations
Venetian discourses: drawn from the history, art & customs of Venice