Postcodes Addressing and Mapping – not as simple as they might seem

1. Postcodes Addressing and Mapping –not as simple as they might seem ESRC Research Methods Festival St Catherine’s College, Oxford 19th July 2006 Robert BarrGeography, School of Environment and Development The University of Manchester Manchester Geomatics robert.barr@manchester.ac.uk

2. Overview • Why social scientists love postcodes • Why they shouldn’t • What postcodes don’t cover • A visual interlude • Why addressing is difficult • Does it matter • A research agenda • Conclusions

3. Why social scientists love postcodes • The UK Postcode system is one of the finest grained systems in the world • Mean number of properties = 14 • Modal number of properties = 1 • Accounted for largely by business postcodes • Maximum number of properties = 99 • Reduced from a small tail of larger numbers recently

4. Why social scientists love postcodes • Most people know their postcode so it is easily captured • It can be easily verified • It occupies a maximum of 7 characters (8 with a space) • This makes the postcode a very efficient surrogate for an address • Usually adding number of building name identifies a single address

5. Why social scientists love postcodes • Most postcodes are stable and persistent • Postcodes have been geographically referenced and the quality of the reference is improving • Postcodes are cross referenced to many other statistical and administrative geographies

6. Why social scientists love postcodes • Postcodes are cross referenced to geodemographic classifications • Postcodes can be cross referenced to other measures such as IMD • Postcodes provide a valuable sampling frame • Postcodes can be handled in spreadsheets, statistical packages and databases – no messy maps!

7. Why they shouldn’t • Many people misquote or invent postcodes • Most postcodes are not verified at point of capture • Most postcodes which change are not updated in official records • e.g. at one stage 10% of postcodes ascribed to GPs in the NHS Codes service were not current on PAF

8. Why they shouldn’t • While things are generally o.k at building level, flats and multi-occupied proprties are less well identified by a postcode • Postcodes are much less reliable at identifying business premises or workplaces • 100,000 postcodes change every month! • Mainly business, but there is a large amount of churn concentrated in particular areas, usually those which are changing and therefore interesting, or for purely postal operational reasons

9. Why they shouldn’t • ONS produces excellent postcode cross reference tables (and keep historic postcodes in the ONSPCD (formerly AFPD) • However this is controlled by the Gridlink consortium (Royal Mail, Ordnance Survey and ONS and is priced to reflect the IPR of RM and OS) reducing use. Quality improving but not perfect. • The PAF and Address Manager are useful complementary products but usage is severely limited by price and licensing arrangements.

10. Why they shouldn’t • The geodemographic or IMD scores attached to postcodes are misleading because of the granularity of postcodes is not reflected in the classifications • While postcodes are cross referenced to other boundaries this can be fuzzy and postcode geography respects no other administrative or statistical geographies • Maps of postcodes, particularly abstract Thiessen polygon based ones are a poor representation of what postcodes represent

11. What postcodes in PAF don’t cover • Easier to say what they do! • 27 million current postal delivery points • These only represent about 60% of buildings that appear on OS map • Many insiginificant sheds or garages • Many very significant • Campuses • Multi-occupied premises • Workplaces – large factories industrial buildings community buildings

12. What postcodes in PAF don’t cover • Easier to say what they do! • 27 million current postal delivery points • These only represent about 60% of buildings that appear on OS map • Many insignificant sheds or garages • Many very significant • Campuses • Multi-occupied premises • Workplaces – large factories industrial buildings community buildings

13. What postcodes in PAF don’t cover • Former delivery points – no history • Future delivery points pre-build and planning data • In short the postcode file is a biased and often inaccurate sampling frame for : “structures where people live or work”

14. Discrepancy map 2001 Census study commissioned by ONS and Manchester City Council

19. Address Points

20. Random grid square Central London

21. Postcodes

22. Postcode Thiessen Polygons

23. Blocks

24. Ordnance SurveyLandLine to MasterMap

26. Why addressing is difficult • The meaning of an address depends on: • The semantic structure – that is the text of the address • The function of the object being addressed • For example, mail delivery point or cadastral parcel

27. Why addressing is difficult • The purpose for which the object is being addressed • For example, delivery, legal definition or navigation, utility connection • The form of the object being addressed • For example House, Flat, Church,, Factory

28. Delivery point Letter Parcel Large Item – e.g. shed Dwelling Taxable hereditament Property – legal In uniform ownership or tenure Property physical Parcel Building Utility connection point Utility billing address Legal sub-parcel Wayleave ‘Point of Interest’ Street furniture Advertising location Infrastructure Bridge Tunnel Emergency services Fire Ambulance PoliceMotoring organisations Etc Etc … What are we addressing?

29. Ontology “An explicit formal specification of how to represent the objects, concepts and other entities that are assumed to exist in some area of interest and the relationships that hold among them.” ( DOI Foundation, 2003).

30. Ontology • Ontologies are important: • They define geographic concepts • Move from fuzzy natural language definitions • … to formal definitions that can be standardised • They are a vital step on the way to a ‘Semantic Web’ • They make it easier to re-use data in new situations

31. Limitations of Ontology • A shared view? • A useful ontology requires the widest possible consensus and use • Ontology creation tools and editors make it easier to re-invent an ontology than to re-use existing ones • While it is theoretically possible to extend an ontology from one domain to another, in practice this is rarely done • Semantically orientated

32. Semantics - Geography - Topology • Address data is complex because it has three elements: • Semantic structure • Data dictionaries / ‘grammar’ / • Geography • An absolute location in space • Representative point, building footprint, property parcel for the represented object • Topology • Street segments, number ranges, blocks

33. Does it matter? • Addressing errors generate an immeasurable and clustered set of errors in statistics based on administrative data sources • The credibility and reputation of the 2001 census was unfairly impugned because of the address related coverage errors in Manchester and Westminster

34. Does it matter? • Outside the research arena poor addressing: • Costs lives (Fire and ambulance despatching) • Increases congestion and pollution • RAC Foundation - 15% of motorists in cities are lost • Makes planning and monitoring programmes such as Housing Market Renewal with a 15 year prospect difficult and unreliable • Costs business (particularly e-business) large sums because of delivery delays and fraud

35. Research Agenda • A theoretical base is required for addressing • The strengths and limitations of direct geographic representation (point, line and area coordinates) in the light of work on error and positional accuracy improvement need to be assessed

36. Research Agenda • The role of topology as the linkage between geometry and semantics needs to be formalised particularly in the background to TIGER • Topologically Integrated Geographic Encoding and Referencing (US Bureau of Census)

37. Research Agenda • The ways in which the concepts of ‘building’, ‘parcel’, ‘block face’, ‘street segment’, ‘block’, ‘street’ and ‘locality’ are used in practice and the conflicts between usages need to be identified • An analysis needs to be carried out of the various, sometimes conflicting, semantic structures for addresses. • The relationship between geographic and mailing addresses needs to be defined more specifically

38. Research Agenda • A triple Ontology is required: • Semantic elements of addresses • e.g. Building Name, Number, Street • Objects referenced by addresses • Delivery point, building, parcel, landmark • The applications of addresses, • Delivery (mail), Identification (cadastral), access (emergency services)

39. Research Agenda • Additional Ontologies • Building Forms: • House • Detached • Semi-detached • Terraced • Flats • Commercial Buildings • Retail • Factory • Warehouse

40. Conclusions • Addresses are not as simple as they look • Addresses are a more important part of SDIs than is often apparent • An international standard for geographic addressing is required to complement the standards for postal addressing

41. Conclusions • Such a standard should be based on research and sound theory • The implementation of such a standard will spatially enable the Semantic Web by making implicit geographical references, in the form of addresses, explicit

42. That’s it! robert.barr@manchester.ac.uk