Data measures
Ordnance Survey measures the data in its products in one or more of the ways set out in the table below:
Definitions of data measures table
Data measure | Definition | Sub-measure | Definition |
---|---|---|---|
Completeness | Presence and absence of features against the specified data content* | Omission | Features representing objects that conform to the specified data content but are not present in the data |
Commission | Features representing objects that do not conform to the specified data content but are present in the data | ||
Logical consistency | Degree of adherence to logical rules of data structure, attribution and relationships | Conceptual consistency | How closely the data follows the conceptual rules (or model) |
Domain consistency | How closely the data values in the dataset match the range of values in the dataset specification | ||
Format consistency | The physical structure (syntax): how closely the data stored and delivered fits the database schema and agreed supply formats | ||
Topological consistency | The explicit topological references between features (connectivity) – according to specification | ||
Positional accuracy | Accuracy of the position of features | Absolute accuracy | How closely the coordinates of a point in the dataset agree with the coordinates of the same point on the ground (in the British National Grid reference system) |
Relative accuracy | Positional consistency of a data point or feature in relation to other local data points or features within the same or another reference dataset | ||
Geometric fidelity | The ‘trueness’ of features to the shapes and alignments of the objects they represent* | ||
Temporal accuracy | Accuracy of temporal | Temporal consistency | How well-ordered events are recorded in the dataset (life cycles) |
attributes and temporal relationships of features | Temporal validity (currency) | Validity of data with respect to time: the amount of real-world change that has been incorporated in the dataset that is scheduled for capture under current specifications | |
Thematic accuracy (attribute accuracy) | Classification of features and their attributes | Classification correctness | How accurately the attributes within the dataset record the information about objects* |
*When testing the data according to the dataset specification against the ‘real world’ or reference dataset.
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