History in the parcel fabric layer
This topic applies to ArcEditor and ArcInfo only.
In many cadastres, the chain of title is essential to the security of the present holder of the title. It is this evidence that validates a claim. A parcel database must not only provide an accurate representation of the current parcel boundaries but also a historic record of changes to the parcel boundaries. In the United States, the validity of title or rights on a parcel of land is based on evidence of previous land surveys and documents (a chain of evidence). Even in countries that guarantee title, the chain of records and boundary delineation is fundamental. New parcel surveys cannot be undertaken unless surveyors have access to previous survey information; survey data and past deeds or titles should never be discarded.
Parcel history and fabric least-squares adjustments
In the parcel fabric, historic parcels are important for both their legal role and their value in fabric adjustments. Historic parcels contain valid dimension data that provides increased measurement redundancy in a fabric least-squares adjustment.
Continued adjustment of the parcel fabric means the point coordinates will change over time. Coordinates are simply the current best estimates of parcel corner locations. To track parcel lineage, the spatial relationship between current and historic parcels must be retained. Therefore, all parcel boundaries, both current and historic, will be part of any least-squares adjustment. Historic parcel boundaries will adjust with current parcel boundaries.
Parcel history and plans
The fabric tracks parcel history by both plan date (date of record of survey) and system date (date parcel changes were entered into the database). When an existing parcel in the parcel fabric is replaced by parcels defined in a new plan or record of survey, the existing parcel and its lines become historic. Parcel corner points don't necessarily become historic when a parcel becomes historic, because adjacent parcels that share the point may still be current.
The fabric stores two start date (legal date and system date) and two end date attributes on parcels and lines. The legal start date corresponds to the date of record of the current parcel's associated plan, and the legal end date corresponds to the date of record of the new, superseding parcels' associated plan. The legal start and end date are user defined and managed. The system start and end dates correspond to the dates parcels were entered into and replaced in the system, respectively.
In the fabric, historic parcels have their Historic attribute field value set to 1 (true). Active or current parcels have their Historic attribute field value field set to 0 (false).
The Historic field is automatically set to 1 in the following cases:
- Parcel merge. Parcels being merged are flagged as historic.
- Parcel division. The parcel being divided is flagged as historic.
- Parcel Remainder. The original parcel is flagged as historic.
- New from parent. The parent parcel is flagged as historic.
The Historic attribute on a parcel can manually be set to 1 (true) in the Parcel Details dialog box or by right-clicking a parcel and clicking Historic.
Parcel fabric history and database archiving
Since historic parcel boundaries participate in continued adjustments of the parcel fabric, history in the parcel fabric is dynamic. This contrasts with an archive of static information that is not edited or altered but simply retained. This is static history. Cadastres and the parcel fabric have both types of information. The recorded parcel dimensions on a historic parcel and any related title records are never altered and are considered static. Coordinates for these parcels change in a least-squares adjustment and are considered dynamic.