Data Quality¶
Positional Accuracy¶
Positional accuracy is an assessment of the closeness of the location of the spatial objects in relation to their true positions on the earth’s surface. In this product positional accuracy refers to horizontal accuracy. The horizontal positional accuracy is the assessed accuracy after all transformations have been carried out.
Horizontal Accuracy¶
The horizontal positional accuracy of Surface Cover data reflects the positional accuracy of source sensors utilised in data collection, and the reliability of feature classification and associated orthogonalisation processes. The horizontal positional accuracy of source imagery varies across collected strips and ranges from +/-0.5m CE90 to +/-2.5m CE90.
The National Surface Cover layer was classified from remotely sensed satellite imagery at a 30-metre grid resolution. The horizontal positional accuracy of source imagery used for the classification of surface cover pixels is +/-12m CE90. The positional accuracy of the National Surface Cover layer pixels will reflect the accuracy of the source imagery from which it was classified as well as the classification process.
Thematic Quality¶
Thematic accuracy is defined as the accuracy of quantitative attributes, the correctness of non-quantitative attributes, and of the classification of features and their relationships.
Classification Correctness¶
Classification correctness is an assessment of the reliability of values assigned to features in the dataset in relation to their true ‘real world’ values.
The rate of classification correctness of the Urban Surface Cover dataset has been measured at above 90%.
The rate of classification correctness of the National Surface Cover dataset has been measured at above 85%.
Logical Consistency¶
Logical consistency is a measure of the degree to which data complies to a technical specification. The test procedures are a mixture of software scripts and manual visual analysis. The data structure of Surface Cover has been tested for conformance to the data model. The following have been tested and confirmed to conform:
File names
Attribute names
Attribute types
Attribute domains
Object type
Topological Consistency¶
Topological consistency is the measure of how features spatially relate to other features within and across the Surface Cover theme. Topological inconsistencies are identified using a combination of automated rules, and visual analysis. Where topological inconsistencies are identified, they are notified back to the supplier for remediation. Some minor topological inconsistencies are corrected during product processing. The level of topological consistency is dependent on the data supplied to Geoscape.
Temporal Accuracy¶
Temporal accuracy is an assessment of both temporal consistency (how well-ordered lifecycle events are) and temporal validity (validity of data with respect to time).
Completeness¶
Completeness is an assessment of the extent and range of the dataset with regard to completeness of coverage, completeness of classification and completeness of verification. Components that makeup Surface Cover includes Dataset, Theme, and Layer Coverage and coverage will be 100% complete across the areas captured to date. The Surface Cover product contains a complete population of the Surface Cover layer.
Attribute Completeness¶
The layers within the Surface Cover have a full population of attributes in accordance with the data model.
Feature Completeness¶
The omission rate of Trees is directly related to the classification correctness of the Urban Surface Cover and the vertical accuracies of the DSM and DTM.
Data Quality Scope¶
All spatial features including their attributes in the current time period for the Surface Cover Dataset.