Requirements
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At the time when this study was undertaken, the Department of Environment (DoE) was much more concerned with urban deprivation, and especially inner city regeneration. In 1975 Sally Holtermann, then a researcher within the DoE, also noticed the ratio bias. She pointed out that if area targeting is seen to be efficient, effective and equitable, then the metrics used should identify areas, where– a high proportion of the local population is deprived (ratios)
– a high proportion of all deprived live (numbers)
– there is a high density of deprived in the area
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As we have already noted, ratios and numbers operationalise only one each of the above requirements.The question is how do we accommodate all these three requirements simultaneously? This was a common problem and there were a variety of graphical solutions, which were not entirely satisfactory.
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For example, Professor Howe, in his 1970 Atlas of Disease and Mortality used :
- Proportional symbols for the number of deaths
- Shading to indicate the Standardised Mortality Ratios. He also used dotted outlines when these ratios were statistically insignificant.
The map becomes cluttered and confusing and it is difficult to discern the more important trends. The shading (here the ratios) tends to dominate. |
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In the days of paper mapping, the map performed several functions which were compromised. With the advent of computers, it became obvious even in the 1970s that the data recording function would soon be subsumed by databases, which will become digital maps – the ultimate reference maps. The visual map could therefore be devoted to the communication of trends in the data.
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