1. Representing Geographic Features

1.1. Introduction

This section introduces the key concepts required to understand how the Geography Markup Language (GML) models the world. It is based on the OGC Abstract Specification (available online: http://www.opengis.org/techno/specs.htm), which defines a geographic feature as “an abstraction of a real world phenomenon; it is a geographic feature if it is associated with a location relative to the Earth.” Thus a digital representation of the real world can be thought of as a set of features. The state of a feature is defined by a set of properties, where each property can be thought of as a {name, type, value} triple. The number of properties a feature may have, together with their names and types, are ...

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