As explained in the previous sections, a latitude/longitude position is in general coded as a gml:pos element (when used in a Point) or as a token of two numerical values in a gml:posList (when used in the definition of a Curve). There are special situations in the aeronautical data when the latitude/longitude position is derived from the position of another feature or when it is necessary to code additional information such as a different accuracy or srsName from the rest of the points of a Curve. In these situations, GML offers the possibility to use a gml:pointProperty instead of a gml:pos element.
Note that the pointProperty allows either referring to another gml:Point (by xlink:href) or providing a gml:Point child element.
According to the GML standard chapter 10 :
A property that has a point as its value domain may either be an appropriate geometry element encapsulated in an element of this type or an XLink reference to a remote geometry element (where remote includes geometry elements located elsewhere in the same document). Either the reference or the contained element shall be given, but neither both nor none.