1. Spatial feature representation

OpenGIS Abstract Specifications 

Start with Topic 0 Overview -Introduction and roadmap to the Abstract specification.

OpenGIS Implementation Specification for Geographic information - Simple feature access - Part 1: Common architecture

It describes the common architecture for simple feature geometry. The base Geometry class has subclasses for Point, Curve, Surface and GeometryCollection. Each geometric object is associated with a Spatial Reference System, which describes the coordinate space in which the geometric object is defined. The extended Geometry model has specialized 0, 1 and 2-dimensional collection classes named MultiPoint, MultiLineString and MultiPolygon for modeling geometries corresponding to collections of Points, LineStrings and Polygons, respectively. MultiCurve and MultiSurface are introduced as abstract superclasses that generalize the collection interfaces to handle Curves and Surfaces.