ISO 19157:2013 Geographic information - Data quality
|Full name||ISO 19157:2013, Geographic information – Data quality.|
|Published by||ISO/TC 211|
|Type of standard||ISO International Standard
|Related standard(s)||ISO 19115-1:2013, Geographic information – Metadata – Part 1: Fundamentals
ISO 19115-2:2009, Geographic information – Metadata – Part 2: Extensions for imagery and gridded data ISO 19158:2012, Geographic information – Quality assurance of data supply
|Application||The standard specifies the description, evaluation and reporting of the quality of geographic data.|
|Data quality evaluation process
Data quality metadata Standalone quality report Data quality measure
ISO 19157:2013 establishes the principles for describing the quality for geographic data. It defines components for describing data quality; specifies components and content structure of a register for data quality measures; describes general procedures for evaluating the quality of geographic data; and establishes principles for reporting data quality.
The standard also defines a set of data quality measures for use in evaluating and reporting data quality. It is applicable to data producers providing quality information to describe and assess how well a dataset conforms to its product specification and to data users attempting to determine whether or not specific geographic data are of sufficient quality for their particular application.
The standard does not attempt to define minimum acceptable levels of quality for geographic data.
ISO 19131:2007 describes in a structured way what the user wants, that is, the specification of the product required. While aimed primarily at specifying required datasets, the standard can also be used to specify services and other geospatial products. The standard is essentially the inverse of ISO 19115:2003 and uses the concepts and metadata elements and entities in ISO 19115:2003. Hence, it means that one can compare a product specification directly and in detail with the metadata of candidate offerings.
As the specification and metadata are both structured and contain many encoded elements, much of the matching can be done automatically, to filter out candidates that do not meet the specification. Candidate products can be obtained from within a user’s domain, but also from elsewhere. Hence, even an expert user might not be aware of possible sources for suitable products. This powerful capability enables of the ISO 19115:2003 and ISO 19131:2007 combination to filter out suitable candidates automatically.
An ISO 19131:2007 product specification can also be used to guide the development of a new product that meets the specification, and for others needing a similar product to see if the proposed product will also meet their needs. In South Africa, for example, the Committee for Spatial Information (CSI) is using ISO 19131:2007 for developing the form to be used by data custodians for informing the CSI of their planned data capture programmes, such as for aerial photography.
While ISO 19131:2007 does include annexes with UML class diagrams and data dictionaries as tables (as is done in ISO 19115:2003), it is probably still necessary for the user to consult ISO 19115:2003 when using ISO 19131:2007, as ISO 19115:2003 has more details about the metadata (and hence, product specification) concepts, elements and entities. ISO 19131:2007 specifies that a data product specification shall describe the following aspects of the product:
- Overview: source and provenance of the specification, relevant terminology and an informal description of the required product, such as the dataset content, spatial and temporal extents, purpose, sources, production processes and maintenance.
- Specification scopes: the scope of the required product, in terms of spatial and temporal extent, feature types, property types, property values, spatial representation, product hierarchy and partitioning (e.g. between the dynamic and static sorts of data in the required product), The concept ‘product hierarchy’ is not defined in the standard, but this applies to each of the partitions of the product being specified, as they can be at different levels: attribute, attribute type, feature, feature type, tile, dataset, series, etc. For each partition, the level code, level name, level description, extent and coverage are to be specified.
- Data product identification: title, abstract, topic category (one of the pre-defined themes that applies to the required product, such as farming, boundaries, elevation or transportation) and geographic description (actually, spatial extent) shall be provided and alternate title, purpose, spatial representation type (e.g. vector or raster), spatial resolution and supplemental information may be provided.
- Data content and structure: feature-based, coverage-based or imagery data. The content of a feature-based product shall be described in terms of an application schema (content, structure and constraints applicable) and a feature catalogue (or classification system). The application schema can be very complicated, catering for relationships between feature, property and attribute types, such as feature operations, feature association, inheritance relations and constraints. Imagery data are a form of coverage and a coverage is a sub-type of a feature, which behaves like a function returning one or more feature attribute values for some point within a spatiotemporal domain. A coverage requires an identifier, a description, the type and additional information.
- Reference systems: the spatial reference system (using coordinates or geographic identifiers) and the temporal reference system.
- Data quality: the data quality requirements, acceptable conformance quality levels and corresponding data quality measures. In ISO 19131:2007, the data quality requirements are specified in terms of ISO 19113 and ISO/TS 19138, but these have now been revised by ISO 19157:2013 (described in 10.7.3).
- Data capture: an optional specification of the sources and processes that shall or may be used for the data capture.
- Data maintenance: an optional specification of the principles and criteria to be applied in maintaining the product, such as maintenance and update frequency.
- Portrayal: an optional specification of the portrayal rules and a set of portrayal specifications, for specifying how the data may be represented graphically. This could be particularly important for a web service, for example.
- Data product delivery: delivery format (e.g. transfer standard) and delivery medium (e.g. CD-ROM). The delivery format details may include the name and version of the format; subset, profile or product specification; structure of the delivery file; language(s) and character encoding. The delivery medium details may include units of delivery (how the data are arranged on the medium), estimated sizes, name of the delivery medium and other delivery information.
- Additional information: a catchall for anything else to be specified for the product, such as constraint information regarding access and use.
- Metadata: the metadata that shall be provided with the product, defined in terms of ISO 19115:2003.
With the publication of ISO 19117:2012, Geographic information – Portrayal, ISO 19157:2013, Geographic information – Data quality, and ISO 19115-1:2014, Geographic information – Metadata – Part 1: Fundamentals, ISO 19131:2007 is due to be revised.