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{{short description|Standard for geographical data}}
{{Use British (Oxford) English|date=December 2011}}
'''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 database]]s and [[geographic information system]]s.
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 [[class (computer programming)|classes]]; this part also defines [[Well-known text representation of geometry|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_".<ref name="KresseDanko2011">{{cite book|author1=Wolfgang Kresse|author2=David M. Danko|title=Springer Handbook of Geographic Information|url=https://archive.org/details/springerhandbook00kres|url-access=limited|year=2011|publisher=Springer|isbn=978-3-540-72678-4|pages=[https://archive.org/details/springerhandbook00kres/page/n108 81]–83}}</ref> The [[open access]] OGC standards cover additionally APIs for [[CORBA]] and [[Object Linking and Embedding|OLE]]/[[Component Object Model|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 segment]]s, adding [[circular interpolation]]s (e.g. [[Arc (geometry)|circular arc]]s) and other features like coordinate transformations and methods for validating geometries, as well as [[Geography Markup Language]] support.<ref name="KresseDanko2011"/>

== Details ==
=== Part 1 ===
{{expand section|date=November 2012}}
The geometries are associated with [[spatial reference system]]s. The standard also specifies [[Attribute (computing)|attributes]], [[Method (computer programming)|methods]] and [[Assertion (computing)|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 <code>someGeometryObject.isEmpty()</code> as in Part 1, SQL/MM uses a <code>ST_IsEmpty(...)</code> 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 ==
{{expand section|date=November 2012}}
Direct implementations of Part 2 (SQL/MM) include:
* [[MySQL]] Spatial Extensions.<ref>{{cite web|url=http://dev.mysql.com/doc/refman/5.1/en/spatial-extensions.html|title=MySQL 5.1 documentation on Spatial extensions|website=mysql.com|access-date=2 April 2018}}</ref> Up to MySQL 5.5, all of the functions that calculate relations between geometries are implemented using [[bounding box]]es not the actual geometries.<ref name="geog583"/> Starting from version 5.6, MySQL offers support for precise object shapes.<ref>{{cite web|url=http://dev.mysql.com/doc/refman/5.6/en/spatial-relation-functions.html|title=MySQL :: MySQL 5.6 Reference Manual :: 12.15.9 Functions That Test Spatial Relations Between Geometry Objects|website=dev.mysql.com|access-date=2 April 2018}}</ref>
* [[MonetDB#GIS|MonetDB/GIS]] extension for [[MonetDB]].<ref name=gis>{{cite web | url = http://www.monetdb.org/Documentation/Extensions/GIS | title = GeoSpatial - MonetDB | date = 4 March 2014}}</ref>
* [[PostGIS]] extension for [[PostgreSQL]], also supporting some of the SQL/MM Spatial features.<ref name="dbs">{{cite book|author1=Wolfgang Kresse|author2=David M. Danko|title=Springer Handbook of Geographic Information|url=https://archive.org/details/springerhandbook00kres|url-access=limited|year=2011|publisher=Springer|isbn=978-3-540-72678-4|pages=[https://archive.org/details/springerhandbook00kres/page/n132 105]–106}}</ref>
* [[SpatiaLite]] extension for [[SQLite]]<ref>{{cite web|url=https://www.gaia-gis.it/fossil/libspatialite/index|title=SpatiaLite: SpatiaLite|website=www.gaia-gis.it|access-date=2 April 2018}}</ref>
* [[Oracle Spatial]], which also implements some of the advanced features from SQL/MM Spatial.<ref name="KothuriBeinat2004">{{cite book|author1=Ravikanth V. Kothuri|author2=Euro Beinat|author3=Albert Godfrind|title=Pro Oracle Spatial|url=https://books.google.com/books?id=lznPB1Q397YC&pg=PA65|year=2004|publisher=Apress|isbn=978-1-59059-383-7|page=65}}</ref>
* [[IBM Db2]] Spatial Extender and [[IBM Informix]] Spatial DataBlade.<ref name="dbs"/>
* [[Microsoft SQL Server]] since version 2008,<ref name="dbs"/> with significant additions in the 2012 version.<ref name="Aitchison2012">{{cite book|author=Alastair Aitchison|title=Pro Spatial with SQL Server 2012|url=https://books.google.com/books?id=NdvJXu7hT8oC&pg=PA21|year=2012|publisher=Apress|isbn=978-1-4302-3491-3|pages=21–23}}</ref>
* SAP [[Sybase IQ]].<ref>http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.dc01964.1602/doc/html/saiq-standards-compatibility-spatial.html SAP Sybase IQ support for spatial data</ref>
* [[SAP HANA]] as of 1.0 SPS6.<ref>http://help.sap.com/saphelp_hanaplatform/helpdata/en/7a/2f4266787c1014a9b6ab6cf937f8ac/content.htm?frameset=/en/7a/2d11d7787c1014ac3a8663250814c2/frameset.htm&current_toc=/en/99/d10e4fdaaf41588480a43478e840d5/plain.htm&node_id=12 SAP HANA Spatial Reference: Supported Import and Export Formats for Spatial Data</ref>

Adaptations include:
* Implementations of the CORBA and OLE/COM interfaces detailed above are mainly produced by commercial vendors maintaining legacy technology.
* [[R (programming language)|R]]: The sf package<ref>{{cite web|url=https://cran.r-project.org/package=sf|title=sf: Simple Features for R|first1=Edzer|last1=Pebesma|first2=Roger|last2=Bivand|first3=Ian|last3=Cook|first4=Tim|last4=Keitt|first5=Michael|last5=Sumner|first6=Robin|last6=Lovelace|first7=Hadley|last7=Wickham|first8=Jeroen|last8=Ooms|first9=Etienne|last9=Racine|date=22 March 2018|access-date=2 April 2018|via=R-Packages}}</ref> 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.<ref>{{cite web|url=https://gdal.org/faq.html#what-is-this-ogr-stuff|title=FAQ: What is this OGR stuff?|website=www.gdal.org|access-date=2 April 2018}}</ref>
* The [[Java (programming language)|Java]]-based [[deegree]] framework implements SFA (part 1) and various other OGC standards.<ref name="ShekharXiong2007">{{cite book|author1=Shashi Shekhar|author2=Hui Xiong|title=Encyclopedia of GIS|url=https://books.google.com/books?id=6q2lOfLnwkAC&pg=PA235|year=2007|publisher=Springer|isbn=978-0-387-30858-6|pages=235–236}}</ref>
* The [[Rust (programming language)|Rust]] library [https://docs.rs/geo-types/latest/geo_types/ geo_types] implements geometry primitives that adhere to the simple feature access standards.<ref>{{Cite web |title=geo_types - Rust |url=https://docs.rs/geo-types/latest/geo_types/ |access-date=2023-03-19 |website=docs.rs}}</ref>
[[GeoSPARQL]] is an [[Open Geospatial Consortium|OGC]] standard that is intended to allow geospatially-[[linked data]] representation and querying based on [[Resource Description Framework|RDF]] and [[SPARQL]] by defining an [[ontology (information science)|ontology]] for geospatial reasoning supporting a small Simple Features (as well as [[DE-9IM]] and [[region connection calculus|RCC8]]) [[RDF Schema|RDFS]]/[[Web Ontology Language|OWL]] vocabulary for [[Geography Markup Language|GML]] and [[well-known text|WKT]] literals.<ref>{{cite journal | last1= Battle | first1= Robert | last2= Kolas | first2= Dave | year= 2012 | title= Enabling the Geospatial Semantic Web with Parliament and GeoSPARQL | journal= [[Semantic Web (journal)|Semantic Web]] | volume= 3 | issue= 4 | pages= 355–370 | publisher= [[IOS Press]] | doi= 10.3233/SW-2012-0065 | url= http://www.semantic-web-journal.net/sites/default/files/swj176_3.pdf | access-date= 21 November 2012}}</ref>

As of 2012, various [[NoSQL]] databases had very limited support for "anything more complex than a bounding box or proximity search".<ref name="geog583">{{cite web|url=https://www.e-education.psu.edu/geog583/node/74| title=Penn State Geography 583: Geospatial System Analysis and Design. Databases. |author=Frank Hardisty |date= Fall 2012}}</ref>

==See also==
* [[DE-9IM]]
* [[Well-known text]]
* [[Well-known binary]]

== References ==
{{reflist}}

== External links ==
* [http://www.opengeospatial.org/projects/groups/sfswg Simple Features SWG]

=== Standard documents ===
* ISO/IEC:
** [http://www.iso.org/iso/catalogue_detail.htm?csnumber=40114 ISO 19125-1:2004 Geographic information -- Simple feature access -- Part 1: Common architecture]
** [http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=40115 ISO 19125-2:2004 Geographic information -- Simple feature access -- Part 2: SQL option]
* OpenGIS 
** [http://www.opengeospatial.org/standards/sfa OpenGIS Implementation Specification for Geographic information - Simple feature access - Part 1: Common architecture (05-126, 06-103r3, 06-103r4)], current version 1.2.1
** [http://www.opengeospatial.org/standards/sfs 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
** [http://www.opengeospatial.org/standards/sfc OpenGIS Simple Features Implementation Specification for CORBA (99-054)], current version 1.0
** [http://www.opengeospatial.org/standards/sfo OpenGIS Simple Features Implementation Specification for OLE/COM (99-050)], current version 1.1

{{Open Geospatial Consortium standards}}
{{ISO standards}}

[[Category:Geographic information systems]]
[[Category:Open Geospatial Consortium]]
[[Category:ISO/TC 211]]
[[Category:Spatial database management systems]]