In a nod to my colleague James Cheshire‘s fascination with cartograms, I’ve created one from the Spatial Equity data I used in the previous post. A cartogram is a map in which the value of each spatial unit’s area is replaced with a thematic mapping value; thus the mapped representation is warped and distorted to reflect the new thematic variable. Danny Dorling has been particularly active in this field, writing up work on Dorling Cartograms in the CATMOG series, and laterly using the Gastner Newman method to create cartograms for his interesting work in the book: The Atlas of the Real World.

Figure 1: Cartogram of Spatial Equity by Gravity Potential Model

It is clear from figure 1 that the south of Southwark suffers in terms of accessibility to a Southwark GP, whereas the central areas, characterised by a higher population density and more social housing have greater accessibility to healthcare services.

Whilst I’m not sure whether such a representation is entirely appropriate in this context, it does tell an interesting story- the same as the previous post but in a different manner, using the size of areas as well.

NB the map is subject to Crown Copyright 2009 Ordnance Survey. An UKBorders/JISC supplied service.

A little while ago I created some basic measures of spatial equity for my main study site in Southwark, London. Spatial equity in this case relates to a measure of the ‘fairness’ of spatial distribution of services. The NHS as a public institution has a requirement in its universal terms of service to provide a fair service to all.

The following maps aim to show how different areas in Southwark, in this case output areas (OAs), have different characterisitics in terms of: the level of primary care provision available, and the distance to centres of primary healthcare. Following Truelove (1993), Talen and Anselin (1998) and Ricketts et al (1994) the first 3 maps use a buffer-approach to spatial equity, whilst the final shows a gravity model approach.

Figure 1: Spatial equity measured with a 500m buffer around GPs

This first map (figure 1) demonstrates that large parts of Southwark do not have access to healthcare services within 500 metres (euclidian distance), whereas the best served areas have access to more than one GP surgery and as many as 24 individual doctors.

Figure 2: Spatial equity measured with a 750m buffer around GPs

Figure two demonstrates that with a 750m buffer most areas are served, although there are still unserved areas, particularly in the south of the borough. The most well-served areas not have access to as many as 48 doctors.

Figure 3: Spatial equity measured with a 1000m buffer around GPs

A 1km buffer still shows areas of Southwark which are unserved, particularly in the south. My recent working paper features a map which confirms that residents of these areas are less likely to use Southwark services than those in the more core areas in the centre of the borough.

Figure 4: Spatial Equity measured by Log of the Gravity Potential

This final map uses a distance decay function rather than a buffer to represent spatial equity and is specified thusly (Talen and Anselin, 1998 p.600):

where Sj is the size of a facility (measured by number of doctors, operating capacity etc.) at location j and d is a distance decay factor between area i and facility j with a friction parameter alpha, here set to 2.

The result is not hugely different to the buffered approaches, giving a similar account of affairs. It is notable that in all cases the spatial equity correlates with provision of social housing. In the UK context Southwark is a special case, being amongst the most deprived Local authorities by IMD07 rank, in which fair access to services is skewed towards the needs of the more deprived, whether or not uptake, or ability to uptake actually reflects this is another question.

References

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