Add a Hierarchy Attribute

The OS MRN data does not contain a specific field for the hierarchy of the network, for example, a numerical value representing the relative importance of a road link, for example, motorway vs. A-road vs. B-road vs. local road. However, the highway attribute in the OS MRN data describes the type of road link and from that a hierarchy can be derived.

Move to the ‘Hierarchy’ tab of the Network Dataset Properties and tick the box next to ‘Add Hierarchy Attribute’ to open the hierarchy attribute settings options.

For the purposes of testing, a 4-tier hierarchy was created by using a field script to look up the highway field value and classify the hierarchy of the link based on the following:

• Hierarchy 1 = motorways

• Hierarchy 2 = primary roads

• Hierarchy 3 = secondary roads

• Hierarchy 4 = local roads

The default value of the hierarchy was set to 4 for all other links. It is not clear at this time what the implications of this might be for non-road travel modes such as rail or foot.

The screenshot below shows the Field Script needed to implement this hierarchy based on the different values in the highway field in the OS MRN data (also available in the accompanying “MRN code snippets.md” markdown file on the OS MRN Downloads page). The second screenshot shows the complete Hierarchy settings screen.

The Hierarchy Field Script.

The completed Hierarchy settings screen with Field Script.