Simple Features (officially Simple Feature Access) is both an Open Geospatial Consortium (OGC) and International Organization for Standardization (ISO) standard ISO 19125 that specifies a common storage and access model of mostly two-dimensional geometries (point, line, polygon, multi-point, multi-line, etc.) used by geographic information systems.
The ISO 19125 standard comes in two parts. Part one, ISO 19125-1 (SFA-CA for "common architecture"), defines a model for two-dimensional simple features, with linear interpolation between vertices. The data model defined in SFA-CA is a hierarchy of classes. This part also defines representation using Well-Known Text (and Binary). Part 2 of the standard, ISO 19125-2 (SFA-SQL), defines an implementation using SQL. The OpenGIS standard(s) cover implementations in CORBA and OLE/COM as well, although these have lagged behind the SQL one and are not standardized by ISO.
The geometries are also associated with spatial reference systems. The standard also specifies attributes, methods and assertions with the geometries. 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 of Simple Feature Access is implemented to varying degrees in: