An airline route map shows a graph illustrated on top of an ordinary map. The
graph is drawn so that its vertices correspond to cities while its edges correspond
to arcs. In the route map context, arc length is a rough-and-ready guide to the
length of the corresponding flight, whether measured in travel time or frequent
flyer miles. This metric property is not reflective of the graph. The length of a
representing arc has no graph-theoretic meaning. Indeed, while an arc contains
infinitely many geometric points, the edge it represents consists of (just) two
vertices.