Data quality

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Spatial data quality elements provide information on the fitness-for-use of a spatial database by describing why, when and how the data are created, and how accurate the data are. The elements include an overview describing the purpose and usage, as well as specific quality elements reporting on the lineage, positional accuracy, attribute accuracy, logical consistency and completeness. This information is provided to users for all spatial data products disseminated for the census.

Lineage

Describes the history of the spatial data, including descriptions of the source material from which the data were derived, and the methods of derivation. It also contains the dates of the source material, and all transformations involved in producing the final digital files or map products.

The 2006 CAR boundary files were created using spatial data from the 2006 Census Consolidated Subdivisions Digital Boundary File and 2006 Province and Territories Cartographic Boundary File. These boundary files are two of 12 boundary file products developed using the following procedures:

Creation of the 2006 Digital Boundary Files

The Spatial Data Infrastructure was used to generate the 2006 Digital Boundary Files by aggregating polygons using geographic codes. For example, to create the digital boundary files for the provinces and territories, all the polygonal units within the Spatial Data Infrastructure with the same relationship to a province or territory were aggregated to form the polygon(s) that represent that province or territory. Additional information (e.g., name) for each geographic area was incorporated into the product from the Spatial Data Infrastructure.

Creation of the 2006 Cartographic Boundary Files

The creation of the 2006 Cartographic Boundary File used the 2006 Digital Boundary Files and a set of hydrographic features from the National Geographic Database. The hydrographic features used included coastal features (e.g., oceans, bays) and the Great Lakes, and the St. Lawrence River. These data were used to remove from the digital boundary files that portion of the geographical area that is within these major coastal water features.

Additional formatting

The files were transformed from Lambert conformal conic projection into latitude / longitude coordinates. Finally, the files were verified, translated into French and English versions and appropriately labelled.

The files were converted into three output formats (ArcInfo® [.shp], Geography Markup Language [.gml] and MapInfo® [.tab]).

Creation of the coastal layer

The coastal layer was created by selecting water features exterior to Canada's land mass from the National Geographic Database's hydrographic reference layers. These reference data were sourced from the National Topographic Data Base (1:50,000 and the 1:250,000 maps) and the Digital Chart of the World. This included polygon features forming the Pacific, Atlantic and Arctic oceans, as well as the Beaufort and Labrador seas and all related channels, straits, passages, inlets and bays including Hudson Bay and James Bay. In addition, features forming the Great Lakes, Lake of the Woods and the St. Lawrence Seaway were also included.

The coastal layer was then generalized by removing all islands smaller than 100,000 square metres except when the islands accounted for the only land area for geographic areas or when they were intersected by road arcs found on the road network file.

Creation of the inland water layer

The inland water layer was created by selecting water features from the National Geographic Database's hydrographic reference layers. These reference data were sourced from the National Topographic Data Base (1:50,000 and the 1:250,000 maps) and the Digital Chart of the World. Each feature was assigned a rank based on its size and/or cultural importance. The largest and most important features have lower rank values. These ranks can be used to select and format features for map display at different scales.

Positional accuracy

Refers to the absolute and relative accuracy of the positions of geographic features. Absolute accuracy is the closeness of the coordinate values in a dataset to values accepted as or being true. Relative accuracy is the closeness of the relative positions of features to their respective relative positions accepted as or being true. Descriptions of positional accuracy include the quality of the final file or product after all transformations.

The positional accuracy of the CAR boundary files are based on the positional accuracy of the source material used in its production.

The source boundaries are derived from the Spatial Data Infrastructure. The data in the Spatial Data Infrastructure are stored in double precision. This precision allows features that are next to each other on the ground to be placed in the correct position on the map, relative to each other, without overlap. However, the absolute positional accuracy of the features in the database varies depending on the source of the features.

The Spatial Data Infrastructure is not a Global Positioning System. However, every possible attempt is made to ensure that the geographic area boundaries maintained in the Spatial Data Infrastructure respect the limits of the administrative entities that they represent (e.g., census division and census subdivision) or on which they are based (e.g., census metropolitan area or census agglomeration). The positional accuracy of these limits is dependent upon source materials used by Statistics Canada to identify the location of limits. In addition, due to the importance placed on relative positional accuracy, the positional accuracy of other geographic data (e.g., road network data and hydrographic data) that are stored within the Spatial Data Infrastructure is considered when positioning the limits of the geographic areas.

Attribute accuracy

Refers to the accuracy of the quantitative and qualitative information attached to each feature (such as population for an urban area, street name, census subdivision name and code).

The attribute data associated with the polygons in the CAR boundary file was verified against the data in the Census Agricultural Regions Attribute File.

Logical consistency

Describes the fidelity of relationships encoded in the data structure of the digital spatial data.

Every polygon was verified to have a valid identifier for the census agricultural region: the CARuid. Every CARuid in the CAR boundary files was verified to be in the CAR Attribute File and have the correct corresponding AGuid (a code that uniquely identifies a CAR and provides a link to the data in 2006 Census of Agriculture data tables).

Completeness

Refers to the degree to which geographic features, their attributes and their relationships are included or omitted in a dataset. It also includes information on selection criteria, definitions used, and other relevant mapping rules.

The number of census agricultural regions as well as their unique identifiers were verified against the information in the CAR Attribute File.