A base unit is a unit of measure that cannot be derived by combination of other base units within a particular system of units. For example, in the SI system of units, the base units are metre, kilogram, second, Ampere, Kelvin, mole, and candela, for the physical quantity types length, mass, time interval, electric current, thermodynamic temperature, amount of substance and luminous intensity, respectively.gml:BaseUnit extends generic gml:UnitDefinition with the property gml:unitsSystem, which carries a reference to the units system to which this base unit is asserted to belong.
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="BaseUnit" type="gml:BaseUnitType" substitutionGroup="gml:UnitDefinition"><annotation><documentation>A base unit is a unit of measure that cannot be derived by combination of other base units within a particular system of units. For example, in the SI system of units, the base units are metre, kilogram, second, Ampere, Kelvin, mole, and candela, for the physical quantity types length, mass, time interval, electric current, thermodynamic temperature, amount of substance and luminous intensity, respectively. gml:BaseUnit extends generic gml:UnitDefinition with the property gml:unitsSystem, which carries a reference to the units system to which this base unit is asserted to belong.</documentation></annotation></element>