Building a routable network

(outline, to be written out)

A geographic file of road geometry is not yet a graph. This page will describe the step from downloaded source data (Network data sources) to a connected, directed network that Dijkstra can traverse.

Planned contents

• From arcs to links and nodes: splitting polylines at intersections, building the node set, and the F1 and F2 from node and to node convention used throughout this wiki
• Planarity and grade separation: crossings that must connect versus bridges and tunnels that must not, and why naive intersection of geometry produces routes through viaducts
• Directionality: one way streets, and representing them as directed links
• Turn restrictions and turn penalties: where they matter, as in urban car routing, and where they can be ignored
• Mode specific subnetworks: filtering links by access rights per mode, and why a pedestrian network is not a subset of a car network
• Connectivity checking: finding disconnected components with connected_parts, and deciding which are genuine islands and which are data errors
• Barriers and crossings: level crossings, ferries and gates

Related

• Network optimisation algorithm, reducing the network once it is built
• Travel speeds per mode, assigning impedance to the links
• Connecting origins and destinations to the network
• GeoDMS network functions