Making Maps Navigable - Programming GPS and OpenStreetMap Applications with Java - page 110

split into links. Currently Europe is typically represented by roughly 100
million links in commercial maps.
For a network, a subset of map data filtered with line attributes, the
link represents the atomic unit of navigation. In terms of network data, a
link is the connection between two manoeuver points.
In normal jargon, a manoeuver describes any special activity on the
steering wheel, like a sharp turn or passing another car. In a navigational
context, a manoeuver point also refers to a point, where the driver can or
has to make a decision to continue his journey: for example, at a normal
intersection: turn left or right or go straight ahead.
Links are also created to assist the driver in unclear trac situations
and the length of a link can range from a few meters to a few hundred
meters with hundreds of shape points. As an example, if you miss an exit
on the German Autobahn, you will have to drive along the link to the next
exit to make a turn manoeuver and drive back to the missed exit. This can
easily cost you 20 to 30 kilometers of extra travel.
Figure 8.1 shows the elements of a digital map:
ˆ Shape points are connected by edges to define geometry.
ˆ Ways are composed of a number of edges.
ˆ Links connect two manoeuver points.
ˆ Destinations are addressable points.
The illustration shows three independent networks connected only by
the destination points. Imagine a person traveling by car, train, or boat
with the freedom to change the vehicle being used in cities. The route from
origin A to destination D defines two links A-C and C-D via manoeuver
point C.
Figure8.1. Entities of a digital map.