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Maps showing overlap between two indicators

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Maps showing overlap between two indicators
The three maps show Local Authorities with (1) high levels of BNP membership, (2) large non-white populations, and (3) both high levels of BNP membership and large non-white populations. The use of the blue, red and overlap purple colours make this a geographic "Venn diagram", allowing viewers to quickly identify areas with high levels on two separate datasets.
Visual types
Level of expertise
Source:
David McCandless "Information is Beautiful" Guardian graphic visualisations series (News)
http://www.guardian.co.uk/news/datablog/2009/nov/06/drugs-bnp
Interactive features
None
Benefits & pitfalls to avoid
  • Shaded maps can emphasise large areas much more than small ones - for example highlighting rural areas over urban, if fixed population areas such as Super Output Areas are shown. Consider providing an alternate mode in which values are represented by circles, or values are scaled by the area size (ie showing density).
  • When using colours to portray data values or types, ensure that the colors used are accessible to all users. Online tools such as ColorBrewer (www.colorbrewer.org) can help identify issues with colours used.
Create your own
  • Chloropleth maps can be created in a range of desktop GIS applications such as MapInfo and ArcGIS.