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Feature types
Layer Structure
In OS MasterMap Topography Layer, features are classified using feature type and feature description attributes. This section describes the feature types and shows their permitted attribution. The tables below provide the following information about each feature type attribute:
Attribute name and definition
The name of the attribute and what it is describing.
Attribute type
The nature of the attribute. The following values may occur:
| Type | Description |
|---|---|
Boolean | Value of ‘true’ or ‘false’. |
Date | Specifies a day within the Gregorian calendar in the format YYYY-MM-DD. |
Integer | Any positive or negative whole number or zero. |
GM_MultiCurve | A set of Polyline geometries. See geometric data types for details. |
GM_Point | A pair of easting and northing coordinates in metres, defining a horizontal location in the British National Grid spatial reference system. See geometric data types for details. |
GM_Surface | A closed area defined by one outer boundary and zero or more inner boundaries (polygon). Each boundary is a closed ring of coordinate pairs, interpolated as for a polyline. See geometric data types for details. |
GM_Curve | An ordered set of points that are connected with a straight line between each pair. See geometric data types for details. |
Real | A floating point number. |
Rectangle | A rectangle defined in the British National Grid. |
String | An ordered set of characters. |
TOID | OS MasterMap unique feature identifier. |
Multiplicity
[1] indicates that the attribute is mandatory and can only occur once. [1..*] indicates that the attribute is mandatory and can occur many times. [0..1] indicates that the attribute is optional; if present, it only occurs once.
[0..*] indicates that the attribute is optional; if present, it can occur many times.
Feature type attributes
The product is comprised of six feature types:
Three of these are topographic feature types: TopographicPoint (such as a post), TopographicLine (such as Mean High Water) and TopographicArea (such as coniferous trees)
One is a boundary feature type: BoundaryLine (such as unitary authority boundary)
Two are cartographic feature types: CartographicSymbol and CartographicText
In addition, if a Change-Only Update (COU) Supply has been provided, the data may contain information about the movement and deletion of features (i.e. Inserts, Updates and Deletes). These are represented by the feature type called DepartedFeature. More information about COU is contained in Section 10 – COU overview.
Each of the six feature types is discussed in more detail in their sub-pages.
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