Settlement hierarchies

A settlement hierarchy answers a simple question for every settlement: how large an area does it dominate? The model answers it with travel time rather than with administrative status, so that the result is comparable between countries with entirely different administrative traditions.

The thresholds

Classifications/Centres_Thresholds defines 25 thresholds. Threshold i corresponds to i times 5 minutes, so the range runs from 0 to 120 minutes in steps of 5. Each threshold has a name of the form L_15min, and those names appear as field names in the output.

The computation

The template is Analyses/Settlement_Hierarchy_T, and it runs per continent.

1. Every settlement centroid is snapped to the nearest node of the final network. A settlement is only accepted when its centroid lies within 100 metres of that node. Settlements that fail this test end up in Unconnected_Settlements and take no part in the hierarchy.
2. An origin to destination matrix is computed over all connected settlements against all connected settlements, cut off at the largest threshold, that is 120 minutes.
3. For each threshold, the model finds for every settlement the most populous settlement reachable within that threshold, and records whether that is the settlement itself. A settlement is therefore a centre at threshold t when no larger settlement can be reached within t minutes.
4. Maxl is the largest threshold at which the settlement is still a centre. It is the single number that summarises the hierarchy.

A settlement that is beaten by a larger neighbour within 5 minutes has Maxl 0. A settlement that is the largest reachable settlement even at 120 minutes is a national scale centre in a sparsely populated territory.

Output

Results are written per continent to %LocalDataProjDir%/Settlement_Hierarchy/all_settlements_<settlement set>/<continent>.shp, with the settlement polygon geometry and the fields:

Field	Meaning
Label	settlement identifier, for example UC___12345
CountryId, Country	country of the settlement
Pop	population of the settlement
Maxl	highest threshold in minutes at which the settlement is a centre

The per threshold indicator columns are also written to a .dbf next to it, one column per threshold name.

The read back version, Hierarchies_ReadOnly, adds the node identifier, the settlement type and a flag telling whether the settlement lies inside an OECD functional urban area. That flag is what the _ex_fua variants in Catchments use.

How it is used further on

Three thresholds have names in the downstream work, used in Accessibility:

Variant	Definition
loc_ctr	centre at 15 minutes
reg_ctr	centre at 30 minutes
nat_ctr	centre at 60 minutes

The catchment variants use thresholds directly: m10 uses the 10 minute threshold, m15 the 15 minute threshold, and so on.

Running it

GeoDmsRun.exe cfg\main.dms /Analyses/Obtain_Settlement_Hierarchies/<continent>/Store_Hierarchies

This has to be done for every continent before any catchment or accessibility run.