Sunday, April 4, 2010

Authoritative Cadastral Data

Unlike other spatial data (hydrography, topography, orthoimagery, etc), cadastral data defines rights and interests in land. Cadastral data are also unique because it is created and maintained by over 4,000 separate entities across the country.

The vision for the National Spatial Data Infrastructure (NSDI) and the National Cadastre within the NSDI is to have a single source of authoritative cadastral data that is controlled and managed by designated data stewards. Access to this data is facilitated by compiling and integrating the data into trusted data sources at state or regional levels. This will reduce duplication of effort and assure that the best available information is used in decision-making.

Cadastral data includes assessment records that support the real estate property tax system, recorded land documents such as deeds and mortgages, indices and summaries of this data such as a grantor-grantee and tract indexes, and survey information captured in plats and surveys.

Authoritative data comes directly from the creator or authoritative source. It is the most current and accurate and has been vetted according to official rules and policy. The data has a known accuracy and lineage and can be verified and certified by data stewards in the authoritative source. In some terminology this is termed the “primary” data source.

Trusted data describes data sets that are published by someone other than the authoritative source and is often the compilation of multiple sources of authoritative data. It is “trusted” because there is an “official process” for compiling the data from authoritative sources and the limitations, currency and attributes are known. The data are often formatted into a standardized form and linkages to the originating source are provided with the data. This trusted source is recognized by the authoritative source as an “official” publisher of this subset. Typically a trusted source is established to integrate data from multiple jurisdictions and to compile it into a standard format. This trusted data is adequate, convenient and cost effective for users who need a regional view and have to deal with multiple sources of data, but there is an understanding of the necessity when final decisions are being made, particularly about rights and interests of specific properties, that the user must go to an authoritative source and acquire authoritative data directly to ensure that they have the most current an accurate data.

Data stewards have the responsibility to organize, collect, maintain and provide data. Data stewards are those closest to the data creation, they have recognized expertise in the field and follow professional standards.

When there is not a single source for data, such as nationwide assessment data which has over 4,000 local government sources, and the effort to acquire authoritative data from individual authoritative sources is impractical, then it is reasonable to acquire trusted data from a trusted source.

All cadastral data collections that do not come from authoritative or trusted sources are “unofficial” or “shadow” copies whose value degrades over time relative to the rate of updates to the authoritative data. Unofficial data is often duplicative and creates redundancy by re-publishing data that are already available from a trusted source. Unofficial sources create confusion among the general consuming public by providing un-maintained duplicative data and “unofficial” parcel-like data sets that can unexpectedly harm or damage property rights with inaccurate out of date information.

Recognizing the importance of authoritative sources for authoritative cadastral data that may be provided through a trusted source will be essential to protect individual land rights, to support local governments and other parcel producers in their authorized role of data stewards and to ensure that the user community has the best available and most current cadastral information.

The FGDC Subcommittee for Cadastral Data, following the directives in OMB Circular A-16, has developed a series of documents over the past ten years that describe the concepts and polices related to the creation, use and publication of cadastral data. There is more information on authoritative and trusted sources for cadastral and data stewards for various components of cadastral data at the FGDC Subcommittee’s publication site (

No comments:

Post a Comment