GEOG3025

Geographical referencing and the modifiable areal unit

problem

GEOG3025

Geographical referencing and the MAUP

• Lecture overview:Objectives of lecture

Introductory questions

Geographical referencing of social data

Modifiable areal unit problem

Lecture summary

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Objectives• To understand that there are

multiple options for the geographical referencing of social data

• To be familiar with the principal datasets and approaches

• To understand the representational difficulties associated with areal aggregation

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Introductory questions…

How do I find out which census area this postcode falls into? What on earth

is the modifiable areal unit problem??

Geographical referencing• Most commonly points and areas• Generally indirect

– Census zones– Service delivery districts– Postal geography– Regular grid (esp. from RS modelling)

• Aggregation from individuals• Arbitrary boundary location cf.

phenomena of interest (‘imposed’ vs ‘natural’ areal units)

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Point data

• Precise location hard to determine• Usually indirect via home address

elements (night-time/day-time)• Point pattern valuable, but mostly

reflects population distribution• Many analysis concepts require

aggregation (rates, denominators etc.)

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Increasing spatial resolution

• Early census data – large zones• Smaller zones, service delivery areas• GIS manipulation of zonal data• Point referencing – indirect and direct• Which is the ‘correct’ spatial object for

the representation of population-related phenomena?

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Representational issues

• Spatial representation is a process, not a single technical decision– Decisions ‘frozen’ in conventional cartography– Digital datasets make possible remodelling of

the data, and linkage between datasets

• Possible to think of the same entities as different types of spatial object

As surface

Disease incidence

As points As lines As areas

What kind of spatial object?

Representation as a process

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Some UK address lists...

• Postcode Address File (Royal Mail)• Council Tax Registers (local

government/Valuation Office Agency)

• National Land and Property Gazetteer (local government/Intelligent Addressing)

• ADDRESS-POINT (Ordnance Survey)

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Points: address referencing

• ~25m postal addresses• Increasing use of address-level

referencing but difficulties achieving national standards (BS7666, Acacia)

• 2001 census difficulties in Manchester and Westminster– 14000 ‘missed’ addresses added to

Manchester 2003 mid-year estimate

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Address matching problems…

• St. Andrews Rd• SO17 1BJ• Flat 3, 9 Winn

Road• Caerdydd• The Haven, Chalk

Dr• 1 Church Hill Drive• Lawn Place, SE15

• Saint Andrew’s Road

• S017IBJ• 9c Winn Road• Cardiff• 379 Chalk Drive• 1 Churchill Drive• Haslam Street,

SE15

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Ambiguous addressesPhoto

: D

ave M

art

in

<West Park, BS8 or Cotham Hill, BS6?>

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Lookup tables

• Giving (population or household weighted) entity-to-entity relationships e.g. postcode to census output area

• Independent from direct effects of imposed areal unit boundaries

• May include coordinate references• Tools for cross-matching geographies• May be generated administratively or

analytically

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UK Lookup tables tool

County District Ward Output Area

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Lookup tables…

• No sliver polygon or spatial mis-matching issues

• May be the only alternative for modelling change over time for detailed geographies

• Source of ancillary variable for areal interpolation (e.g. redistribute unemployment pro rata population counts)

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Modifiable areal unit problem

• Openshaw (1984)• Applicable to all imposed areal

units• Scale and aggregation effects• Always impacts on spatial analysis• Effects often ignored

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Aggregation

Scale

MAUP illustrated

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MAUP

• If we change the boundaries of an areal unit, would we alter the population ‘captured’ to the extent that we would change– Its geodemographic classification– Its position in a deprivation league table

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Ecological fallacy

• Relationships observed in ecological data would not necessarily hold at other scales of aggregation

• Relationships observed in ecological data do not necessarily apply at the individual level

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Ecological data issues

• Are all the people living in a deprived ward ‘deprived’?

• Are all the people living in a ‘well-off retirees’ neighbourhood either well-off or retired?– Almost certainly not!

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Lecture summary

• Ambiguity of geographical referencing• Different spatial data types• Multiple address referencing options• Lookup tables, particularly based on

postcode geographies• Modifiable areal unit and ecological

fallacy issues