science

Simple Features

Simple Features is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Simple Features rather than just read about it. In short: Simple Features (officially Simple Feature Access) is a set of standards that specify a common storage and access model of geographic features made of mostly two-dimensional geometries (point, line, polygon, multi-point, multi-line, etc.) used by geographic databases and geographic information systems. It is formalized by both the Open Geospatial Consortium (OGC) and the International Organization for Standardizatio…

Key takeaways

Simple Features belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Simple Features to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Simple Features from memory before moving on to harder problems.

Reference excerpt

Simple Features (officially Simple Feature Access) is a set of standards that specify a common storage and access model of geographic features made of mostly two-dimensional geometries (point, line, polygon, multi-point, multi-line, etc.) used by geographic databases and geographic information systems. It is formalized by both the Open Geospatial Consortium (OGC) and the International Organization for Standardization (ISO). The ISO 19125 standard comes in two parts. Part 1, ISO 19125-1 (SFA-CA for "common architecture"), defines a model for two-dimensional simple features, with linear interpolation between vertices, defined in a hierarchy of classes; this part also defines representation of geometry in text and binary forms. Part 2 of the standard, ISO 19125-2 (SFA-SQL), defines a "SQL/MM" language binding API for SQL under the prefix "ST_". The open access OGC standards cover additionally APIs for CORBA and OLE/COM, although these have lagged behind the SQL one and are not standardized by ISO. There are also adaptations to other languages covered below. The ISO/IEC 13249-3 SQL/MM Spatial extends the Simple Features data model, originally based on straight-line segments, adding circular interpolations (e.g. circular arcs) and other features like coordinate transformations and methods for validating geometries, as well as Geography Markup Language support.

Details

Part 1

The geometries are associated with spatial reference systems. The standard also specifies attributes, methods and assertions with the geometries, in the object-oriented style. In general, a 2D geometry is simple if it contains no self-intersection. The specification defines DE-9IM spatial predicates and several spatial operators that can be used to generate new geometries from existing geometries.

Part 2 Part 2 is a SQL binding to Part 1, providing a translation of the interface to non-object-oriented environments. For example, instead of a someGeometryObject.isEmpty() as in Part 1, SQL/MM uses a ST_IsEmpty(...) function in SQL.

Spatial The spatial extension adds the datatypes "Circularstring", "CompoundCurve", "CurvePolygon", "PolyhedralSurface", the last of which is also included into the OGC standard. It also defines the SQL/MM versions of these types and operations on them.

Implementations

Direct implementations of Part 2 (SQL/MM) include:

MySQL Spatial Extensions. Up to MySQL 5.5, all of the functions that calculate relations between geometries are implemented using bounding boxes not the actual geometries. Starting from version 5.6, MySQL offers support for precise object shapes. MonetDB/GIS extension for MonetDB. PostGIS extension for PostgreSQL, also supporting some of the SQL/MM Spatial features. SpatiaLite extension for SQLite Oracle Spatial, which also implements some of the advanced features from SQL/MM Spatial. IBM Db2 Spatial Extender and IBM Informix Spatial DataBlade. Microsoft SQL Server since version 2008, with significant additions in the 2012 version. SAP Sybase IQ. SAP HANA as of 1.0 SPS6. Adaptations include:

Implementations of the CORBA and OLE/COM interfaces detailed above are mainly produced by commercial vendors maintaining legacy technology. R: The sf package implements Simple Features and contains functions that bind to GDAL for reading and writing data, to GEOS for geometrical operations, and to PROJ for projection conversions and datum transformations. The GDAL library implements the Simple Features data model in its OGR component. The Java-based deegree framework implements SFA (part 1) and various other OGC standards. The Rust library geo_types implements geometry primitives that adhere to the simple feature access standards. GeoSPARQL is an OGC standard that is intended to allow geospatially-linked data representation and querying based on RDF and SPARQL by defining an ontology for geospatial reasoning supporting a small Simple Features (as well as DE-9IM and RCC8) RDFS/OWL vocabulary for GML and WKT literals. As of 2012, various NoSQL databases had very limited support for "anything more complex than a bounding box or proximity search".

See also DE-9IM Well-known text Well-known binary

References

External links Simple Features SWG

Standard documents ISO/IEC: ISO 19125-1:2004 Geographic information -- Simple feature access -- Part 1: Common architecture ISO 19125-2:2004 Geographic information -- Simple feature access -- Part 2: SQL option OpenGIS OpenGIS Implementation Specification for Geographic information - Simple feature access - Part 1: Common architecture (05-126, 06-103r3, 06-103r4), current version 1.2.1 OpenGIS Simple Feature Access - Part 2: SQL Option (99-054, 05-134, 06-104r3, 06-104r4), current version 1.2.1, formerly OpenGIS Simple Features [Implementation Specification] for SQL OpenGIS Simple Features Implementation Specification for CORBA (99-054), current version 1.0 OpenGIS Simple Features Implementation Specification for OLE/COM (99-050), current version 1.1

Worked examples

Example 1 — a first encounter with Simple Features

Start with the simplest possible case. Write down what Simple Features claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Simple Features before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Simple Features ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Simple Features

In research: Simple Features appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Simple Features in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Simple Features is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geographic information systems, ISO/TC 211, Open Geospatial Consortium, so understanding it makes those chapters shorter.
In everyday life: Look for Simple Features outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Simple Features in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Simple Features means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Simple Features out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Simple Features in simple terms?

Why does Simple Features matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Simple Features?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Simple Features.