Link Topology-Geometry Model
In the road-topology-geometry layer of HERE Lanes, each Link is a polyline connecting exactly two Nodes. Links can have additional Shape Points connected by polylines to provide generalized road centerline geometry. Nodes and Shape Points have latitude and longitude positioning.
This Link-Node topology uses the HERE "stable topology" principle: Each Node represents an intersection (or dead-end). Hence, the base topology of the road network is a simplified Link and Node network that models only intersection-to-intersection connectivity. This HERE Lanes topology model is different from the topology mode in the HERE Infotainment Map in the sense that Infotainment links are aggregated in this new model to be truly intersection to intersection (or dead-end).
This topology-focused approach minimizes changes in the topology model over time. Nodes and Links are modified only when road connectivity actually changes through the addition of new intersections, not for any attribution changes. Links and Nodes are allocated unique references that are stable across map versions, unless a topological change occurs. When that occurs, only the modified elements have new references assigned.
A Node is a point with latitude and longitude position at a resolution of 0.00001°. A Node also has a "Z-level" representing its relative height with respect to other Nodes at roughly the same latitude/longitude. Only one Node can be defined at any given latitude/longitude/Z-level. If there are two or more points at a given latitude/longitude, one will have Z-level = 0; other Z-levels will range from -5 to +5. Larger Z-levels indicate higher relative elevations, and negative Z-levels represent lower relative elevations. A Node must be attached to at least one Link.
A Link is a directed polyline connecting two Nodes with optional intermediate Shape Points. The logical orientation of a Link is defined as being from its starting Node to its ending Node. This orientation is not related to the direction of travel on the link. However, directional attribution such as direction of travel or speed limit references Links relative to this logical orientation. A given Node may be both a start and end Node for different Links adjoining it.
A Link may optionally contain Shape Points along its length to help refine its representation of curved roads. Like Nodes, Shape Points have a latitude and longitude with resolution of 0.00001° (sometimes 10-7 degrees), and a Z-level; the Z-level is always 0 unless there are multiple points at the same location. A shape point always belongs to exactly one Link.
Example: Consider the simple road topology in the first figure below. This topology is represented as Links, Nodes, and Shape Points as shown in the second figure below, in which Links are depicted as lines, Nodes as squares, and Shape Points as circles.