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ISO 28258: Digital Exchange of Soil-Related Data (SoilML)
A comprehensive guide to ISO 28258:2013/Amd.1:2019 for soil data interoperability
Introduction to ISO 28258 and the SoilML Framework
ISO 28258, first published in 2013 and amended in 2019, establishes a standardized framework for the digital exchange of soil-related data. Developed by ISO/TC 190 (Soil quality), this standard defines the SoilML information model built upon the ISO 19156 observation and measurement paradigm. The amendment introduced critical refinements including the renaming of key classes (e.g., “Profile” to “SoilProfile”) and alignment with ISO 19157 for data quality metadata.
The SoilML schema uses GML (Geography Markup Language) as its foundation, ensuring seamless interoperability with existing geospatial data infrastructures and the broader ISO 19100 family of geographic information standards.
At its core, ISO 28258 defines an object-oriented information model where soil observations are linked to spatial features. The model supports the entire workflow from project-level metadata through site characterization, soil profile description, sampling, and laboratory analysis. Each data element carries explicit spatial referencing, depth information, and measurement units, enabling unambiguous data exchange between different organizations and software systems.
| Feature Type | Description | Subtypes |
|---|---|---|
| Project | Background information for soil studies | — |
| Site | Defined area subject to soil investigation | — |
| Plot | Elementary area for observations/sampling | Surface, TrialPit, Borehole |
| SoilProfile | Vertical succession of horizons/layers | — |
| ProfileElement | Abstract base for Layer and Horizon | Layer, Horizon |
| SoilSpecimen | Physical sample taken for analysis | — |
| SoilObservation | Measurement or observation result | — |
| SoilMap | Spatial representation of soil types | — |
Engineering Design Insights for Soil Data Systems
Implementing ISO 28258 in environmental information systems requires careful architectural planning. The standard mandates that all soil-related data use the “ISO 28258” XML namespace when combined with other data types. The class hierarchy reveals a deliberate separation between spatial sampling features (Site, Plot with subtypes Surface/TrialPit/Borehole) and observational data, allowing flexible integration of legacy datasets.
The amendment clarifies that observations are restricted to specific feature types: Site, Plot, SoilProfile, ProfileElement, and SoilSpecimen. Data providers must ensure their extensions comply with these constraints to maintain interoperability.
For depth measurements, ISO 28258 defines a custom Depth data type supporting both simple values (e.g., “60 cm”) and depth extents (e.g., “60-70 cm”). This flexibility is crucial for representing horizon boundaries in soil profiles. Units of measure are mandatory on all depth elements, following the approach used in ISO 19115-1 and ISO/TS 19139.
Extensibility and Provider-Specific Adaptations
A key engineering insight is the standard’s explicit support for extension. Data providers can extend SoilML classes with provider-specific properties while maintaining schema validity. For example, a Plot can be extended with elevation (becoming XYPlot), and a Horizon can be extended with humus content and colour properties. This balance between standardization and flexibility makes ISO 28258 suitable for both regulatory reporting and research applications.
The 2019 amendment added support for SoilMappingUnit geometry as a GM_Object attribute (0..* multiplicity), enabling more precise cartographic representation of soil map units. This is a significant improvement for GIS integration.
Practical Applications and Data Exchange Workflows
ISO 28258 supports multiple common data exchange scenarios: project-level context transfer, site characterization data, soil profile descriptions with horizon-level detail, sample tracking with preparation processes (including transport and storage), and observation results with full provenance metadata. The standard references the ISO 19156 Observation model where each observation has a phenomenon time, result time, procedure, observed property, feature of interest, and result value.
The accompanying XML schema (SoilML.xsd) provides concrete implementation guidance. Namespace imports include GML 3.2, OGC Observations and Measurements 2.0, and sampling feature schemas. This comprehensive approach ensures that soil data exchanged using ISO 28258 can be integrated into broader environmental data platforms.
Frequently Asked Questions
Q1: What is the difference between a Layer and a Horizon in ISO 28258?
A: Layers develop through non-pedogenic processes (geogenesis or anthropogenic action) and may contain multiple horizons. Horizons develop through pedogenic processes within layers. Both are subclasses of ProfileElement and share basic properties like upper/lower depth and ordering within the soil profile.
A: Layers develop through non-pedogenic processes (geogenesis or anthropogenic action) and may contain multiple horizons. Horizons develop through pedogenic processes within layers. Both are subclasses of ProfileElement and share basic properties like upper/lower depth and ordering within the soil profile.
Q2: Can ISO 28258 be used for international soil data exchange?
A: Yes. The standard uses GML as its encoding format, which is an OGC international standard. The ISO 19100 family provides geographic foundation, while the SoilML schema defines soil-specific extensions. This layered approach enables global interoperability.
A: Yes. The standard uses GML as its encoding format, which is an OGC international standard. The ISO 19100 family provides geographic foundation, while the SoilML schema defines soil-specific extensions. This layered approach enables global interoperability.
Q3: How does the 2019 amendment affect existing implementations?
A: The amendment renames several key classes (Profile to SoilProfile, SF_Process to OM_Process) and adds new capabilities like SoilMappingUnit geometry. Existing implementations should update their XML schemas and data files to align with version 2.0 of the SoilML namespace.
A: The amendment renames several key classes (Profile to SoilProfile, SF_Process to OM_Process) and adds new capabilities like SoilMappingUnit geometry. Existing implementations should update their XML schemas and data files to align with version 2.0 of the SoilML namespace.
Q4: What validation tools are available for ISO 28258 data?
A: The standard describes validation software (check tools) in Clause 8. Implementers can validate their XML instances against the SoilML.xsd schema. Additional validation may check domain-specific constraints defined in the data model.
A: The standard describes validation software (check tools) in Clause 8. Implementers can validate their XML instances against the SoilML.xsd schema. Additional validation may check domain-specific constraints defined in the data model.
