made to accommodate secondary indexes based, for example, on street addresses, names, or geographic codes through the use of cross-referenced indexes.

Control of New Parcel Numbers

While the choice of a parcel-identifier system is of fundamental concern, attention must be directed to the allocation and subsequent control of these identifiers. Any parcel-identifier system can only work if one agency has the sole authority for assigning identifiers. This preferably should be that agency responsible for land registration.

During the course of implementing the multipurpose cadastre. the parcel identifier should be introduced during the first phase of the cadastral-mapping program. Assignment of a parcel identifier should be provisional until the cadastral maps are formally approved and registered.

The control of the subsequent allocation, re-allocation, and withdrawal of parcel identifiers is but part of the larger process of managing land-tenure changes. If the configuration of a parcel is changed (e.g., typically by subdivision), that parcel ceases to exist, and new identifiers are assigned to the new parcels. However, the original parcel remains as a historic entity. and the descriptions of it that were entered in the various registers and files when it did exist remain coded to it. Indexes that identify such “retired” parcels must be included in the records system unless provided otherwise by statute.

A special problem with the parcel-identifier system concerns the possibility of error in data processing. There are various techniques available for monitoring the fidelity of a parcel identifier from the time of its initial assignment through subsequent processing, most of which employ the addition of a redundant check digit. The simplest approach is the addition of a check digit at the end of an identifier, which is mathematically related to the sequence of digits in the identifier.

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