A Link is a topological LineString item that stores data regarding its topological relationship with other topological items.

A Link item is a sub-class of a LineString item that is created using Link (Topology > Build). A Link item has a Node item at each end.

Link items are also used to define the geometry of TopoLineString and TopoPolygon items, and can be created as a side-effect of creating TopoPolygon items.


  • Automatic: _bAuto&
    Was the Node item automatically created? Automatic Node items may be automatically deleted in future when associated Link items are edited or deleted.

  • Closed: _closed&
    Does the geometry of the item form a closed loop?

  • Direction flags: _fDirection&
    The restrictions on flow direction of a Link item. This affects the route finding algorithm. By default a Link item can be followed by the route finding algorithm in both directions.
    0 (Both) = Two way, i.e. there are no direction restrictions.
    1 (In) = One way, i.e. from start to end mode.
    2 (Out) = Other way, i.e. reverse direction to "1 (In)" above.
    3 (None) = Neither direction allowed, i.e. link cannot be routed along, it is closed.

  • End node: _id2&
    The ID of the Node item at the end of the Link item.

  • Geometry class: _classGeom$
    The C++ class used to store an item's geometry. This is handled automatically. You can see what precision an item's geometry is stored with by recognising the geometry classes.

  • Number of coverages: _nCoverage&
    The number of "coverages" in which a Link is used.

  • Number of seeds: _nSeed&
    The number of TopoPolygon or TopoLineString items of which this Link item forms part.

  • Number of vertices: _np&
    The number of vertices in the item's geometry.

  • Seeds: _seeds$
    The topological TopoLineString and TopoPolygon items which a Link item forms part of.

  • Start node: _id1&
    The ID of the Node item at the start of the Link item.