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Replica plating transfers samples from corresponding biological colonies or patches to several growth conditions while preserving their spatial arrangement. A master plate makes it possible to relate growth or failure at one location to the same source population on another plate.

The master preserves the source biological colonies; each replica tests a sample of their biological cells. A fabric carrier takes one spatial impression from the master and deposits samples onto fresh plates. Different cell culture medium formulations can then reveal different growth phenotypes at corresponding sites. The carrier copies locations, not a guaranteed number of biological cells. Replica plating spatial correspondence therefore lets an investigator connect a readout to a recoverable source without treating every empty replica site as a missing master biological colony.

The useful trick is that a destructive or growth-restricting test can interrogate one sample while another remains available. In indirect selection of bacterial mutants, the replica supplies information about which source to recover. This also makes a failure-to-grow phenotype accessible: a missing replica biological colony cannot be picked, but its source may still be present on the master. Matching positions is the bridge between testing and retrieval.

Replica plating spatial correspondence is the preserved association between a master site and its sampled sites on replicas. Label a master site by an ordered pair $(r,c)$, specifying its row and column. Keeping the same orientation and viewing convention makes that label refer to the same source on every plate. The biological colonies need not have identical outlines, because the transferred samples can contain different numbers of biological cells.

A simple orientation check shows why a circular outline is insufficient. In a constructed four-by-four layout, a half-turn sends $(r,c)$ to $(5-r,5-c)$. Thus B2, or $(2,2)$, would be confused with C3, or $(3,3)$. Applying the half-turn twice returns the original ordered pair, but applying it once generally selects the wrong source. An asymmetric orientation mark fixes that ambiguity. Two contact transfers also preserve the handedness when all plates are viewed from the same side: any reflection in going from plate to fabric is undone in going from fabric to plate. A fabric-side view must not be silently substituted for a plate-side view.