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

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.

Road layer

The data in the road layer were derived from Statistics Canada's Spatial Data Infrastructure environment based on a copy of the National Geographic Database. The National Geographic Database is a spatial database that contains the road network in Canada, as well as road attributes (name, type, direction, and address ranges).

Road information was incorporated from a variety of other sources, including municipal maps and road data from private companies. However, the timeliness of the National Geographic Database varies from region to region depending on the source data. See Appendix F.

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.

Absolute positional accuracy

Absolute positional accuracy describes the degree to which the position of features in a geographic database reflects their true position on the ground (i.e., the closeness of reported coordinate values to values accepted as true).

The information present in the Spatial Data Infrastructure road layer is provided for the purposes of statistical analysis and census operations only. The absolute position of roads on the Spatial Data Infrastructure varies with the source files and documents used to build and maintain the database. Therefore, the Spatial Data Infrastructure is not suitable for high precision measurement applications such as engineering, property transfers, or other uses that might require highly accurate measurements of the earth's surface.

Absolute positional accuracy is not a requirement for electoral and census processes.

Relative positional accuracy

Relative positional accuracy describes the degree to which the position of features in a geographic database reflects their true ground relationships.

For the National Geographic Database, relative positional accuracy is important. A road must appear in the proper position relative to other roads and physical features.

Attribute accuracy

Attribute accuracy refers to the accuracy of quantitative attributes and the correctness of non-quantitative attributes. Two road attributes were tested for accuracy: road name (name) and road address range. Road address range considers the completeness of addressing on individual arcs.

Road name

During the build phase, every effort was made to insure a proper transfer and association of a specific attribute (i.e., name, type, direction, and address range) to a specific geometric feature. This includes the association as well as its accuracy.

Information on road names and address range attributes within the Road Network File are presented in Table 4.1.

Logical consistency

Logical consistency refers to the fidelity of relationships between all variables in a dataset. For example, a road arc that does not have a road name should not have a road type.

During the build phase, the National Geographic Database dataset was thoroughly tested for logical consistency. Any violations of logical consistency were corrected.

Node-line-area relationships satisfy topological requirements as specified in the ArcInfo® data model.

Consistency with other products

The position of the arcs in the 2010 Road Network File is not necessarily consistent with 2006 and 2001 boundary and road network files.

Completeness

Completeness refers to the presence or absence of features, their attributes and relationships. Many new road features that were not previously found on earlier digital files at Elections Canada and Statistics Canada have been added to the National Geographic Database in order to create a more complete National Geographic Database road layer for all of Canada.

Roads

Features not found in previous road network file products were added to the current Road Network File in order to improve nation-wide road coverage. Table 4.1 shows the number of road features on the current Road Network File.

Table 4.1 Number of road features in the 2010 Road Network File