5. Data quality

Lineage
Positional accuracy
Attribute accuracy
Logical consistency
Consistency with other products
Completeness

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 quality elements include an overview reporting on the lineage, positional accuracy, attribute accuracy, logical consistency and completeness. This information is provided to users for all spatial data products disseminated.

Lineage

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.

The National Geographic Database (NGD) is a joint Statistics Canada-Elections Canada initiative to develop and maintain a spatial database which serves the needs of both organizations. The focus of the NGD is the continual improvement of quality and currency of spatial coverage using updates from provinces, territories and local sources. The source files used for the creation of the 2012 Census Subdivision Boundary File reside on Statistics Canada's Spatial Data Infrastructure (SDI) which is derived directly from data stored on the NGD.

The Census Subdivision Boundary File was created from the lowest level of geography maintained in the SDI. Primary data manipulation of the product file included preserving the geographic hierarchy of the attributes inherent within a geographic level. The census subdivision spatial file was copied into a File Geo Database to facilitate geo-processing (e.g., joins, transforming and verification operations).

The file was verified for spatial and attribute content, translated into French and English, and appropriately named according to the file naming convention. The standard geographic area unique identifier, name, type, and the relationships among the various geographic levels are found in the SDI.

Final data processing consisted of the conversion from the File Geo Database format, using FME^® (Safe Software), into the following GIS file formats: ArcGIS^® (.shp), Geography Markup Language (.gml) and MapInfo^® (.tab).

Positional accuracy

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 Spatial Data Infrastructure is not Global Positioning Systems (GPS)-compliant. However, every possible attempt is made to ensure that the standard 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 standard geographic areas.

Attribute accuracy

Attribute accuracy refers to the accuracy of the quantitative and qualitative information attached to each feature (e.g., census subdivision unique identifier, name, type).

As noted under Lineage, the attributes (names, types and unique identifiers) for all standard geographic areas are sourced from Statistics Canada's Spatial Data Infrastructure. The names and types of standard geographic areas have been updated using source materials from provincial, territorial and federal authorities.

The attribute data associated with the polygons in the 2012 Census Subdivision Boundary File were verified against data in the Spatial Data Infrastructure and found to accurately reflect data stored in the SDI.

Logical consistency

Logical consistency describes the fidelity of relationships encoded in the data structure of the digital spatial data.

The 2012 Census Subdivision Boundary File was verified against data in the Spatial Data Infrastructure and found to be logically consistent.

Consistency with other products

Topology checks were performed with the 2012 Road Network File and the 2012 Census Subdivision Boundary File to measure the degree of integration amongst these products. The results indicated the degree of integration was within the default tolerance parameters as defined below.

• Tolerance: 0.005714285714286 metres
• Resolution: 0.002857142857143 metres

Completeness

Completeness refers to the degree to which geographic features, their attributes and their relationships are included or omitted in a dataset.

The 2012 Census Subdivision Boundary File contains the complete set of standard geographic areas for this level of the geographic hierarchy. Users should be aware that individual census subdivisions may consist of two or more geographic parts.