gml:LinearCS is a one-dimensional coordinate system that consists of the points that lie on the single axis described. The associated coordinate is the distance – with or without offset – from the specified datum to the point along the axis. A LinearCS shall have one gml:axis property element.
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
Source
<element name="LinearCS" type="gml:LinearCSType" substitutionGroup="gml:AbstractCoordinateSystem"><annotation><documentation>gml:LinearCS is a one-dimensional coordinate system that consists of the points that lie on the single axis described. The associated coordinate is the distance – with or without offset – from the specified datum to the point along the axis. A LinearCS shall have one gml:axis property element.</documentation></annotation></element>