ONS Completeness Metrics

This process describes one method of testing the level of mapping completeness for an area in the UK, using information from the Office of National Statistics, downloads from XAPI and evaluation using the measurement plugin for JOSM. The values quoted for the test area are only valid for a similar urban area. The metrics for rural areas or other countries will be different.

Test case, Birmingham

10 urban parliamentary wards were selected in northeast Birmingham. This area is believed to be 100% complete in terms of the road network because all of it has been systematically mapped by Blackadder. Even if a few roads are missing here and there they are counterbalanced by new streets which have been built and mapped since the 2001 census, which is used as a reference for some of the other data.

ONS references

You can obtain population and other information for a given authority or ward here

After entering the name of the location and hitting search click on the "2001 Census: Census Area Statistics" for the population data.

You may also want to know how many households there are, scroll down the original list to "Housing Stock (UV53)" and note the occupied housholds.

Another useful statistic is the "Area of road". You can get this by going back to the list again and typing "Area of road" in the search box on the right hand side.

XAPI call

The main API can't be used for large area downloads because of bbox limits. Use XAPI instead. It also allows us to filter the data so that we only get what we need.

The bbox required for the 9 Birmingham wards making up the area to the north of the M6 plus Perry Barr ward to the south of the motorway was:

         52.6092
-1.9344          -1.7286
         52.5042

Highway types required:

[highway=motorway|motorway_link|trunk|trunk_link|primary|primary_link|secondary|tertiary|unclassified|residential|service]

Call to XAPI:

wget http://www.informationfreeway.org/api/0.6/way[highway=motorway|motorway_link|trunk|trunk_link|primary|primary_link|
secondary|tertiary|unclassified|residential|service][bbox=-1.9344,52.5042,-1.7286,52.6092] -O Birmingham_10_Wards.osm

BUT the server needs UTF-8 encoding on the URL, so:

wget http://www.informationfreeway.org/api/0.6/way[highway=motorway%7Cmotorway_link%7Ctrunk%7Ctrunk_link%7Cprimary
%7Cprimary_link%7Csecondary%7Ctertiary%7Cunclassified%7Cresidential%7Cservice][bbox=-1.9344,52.5042,-1.7286,52.6092] 
-O Birmingham10Wards.osm

Processing the data

Fire up JOSM and make sure the "measurement" plugin is active, then load the downloaded .osm file. You can then see what you have got and ensure that you have all the highways for the area you expect. You can if you wish clip/delete the ways manually to better reflect the area for which you have ONS or other statistics. If you do edit the data in this way be sure that you DO NOT UPLOAD the changes to the main OSM database. For most individual towns and cities a reasonable result should be returned even with a small amount of extra data outside the target area.

Select all the data in the area and then in the selection list select only the ways. Once you have done this you can read off the "Selection Length" from the measurement window which will confirm the total length of highways in the selected area. If you include the nodes in the selection the Selected Length value returned is incorrect.

Findings for Birmingham test area

• Population from ONS = 252,870
• Occupied Households from ONS = 106,068
• Total land area from ONS = 93914 (m2)(thousands)
• Area of Road from ONS = 8976 (m2)(thousands)
• Length of highways in OSM database = 836,035m (Anything lesser than "service" ignored)

So, the two main metrics I plan to use are:

The average road width (calculated from the above) is 10.74m. Using this value for other locations should enable the "Area of Road" statistics from ONS to be roughly transcribed to the total length of road for the given area.

There is 3.306m of highway per head of population.

UK City Progress

Work in progress. Using the above process to report UK town and city progress compared against the above test case.

Length of highway in OSM database per head of population.

Control locations (100 % complete)

• Birmingham (test area only) 836.034km = 3.306m per head of population (252870)
• Cambridge 404.084km = 3.712m per head of population (108863)

Other locations

UK Town Progress

Control locations (100 % complete)

• Swaffham, Norfolk 59.038km = 8.513m per head of population (6935) - Swaffham is a small rural market town