The use of cartograms for BGS data and information representation GeoScience Products and Services Directorate Internal Report IR/13/052 BRITISH GEOLOGICAL SURVEY GEOSCIENCE PRODUCTS AND SERVICES DIRECTORATE INTERNAL REPORT IR/13/052 The use of cartograms for BGS data and information representation The National Grid and other Ordnance Survey data © Crown Copyright and database rights C E Cartwright & H W Holbrook 2013. Ordnance Survey Licence No. 100021290. Keywords Report; Cartograms; Infographics; Statistics; Spatialdata; GIS; Cartography; Communication; Visualization; Choropleth; maps; MAUP. Front cover Cover picture showing a stylised cartogram of world gold production in the context of political stability 2010. Bibliographical reference C E CARTWRIGHT & H W Holbrook. 2013. The use of cartograms for BGS data and information representation. British Geological Survey Internal Report, IR/13/052. 33pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2013. All rights reserved Keyworth, Nottingham British Geological Survey 2013 BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at British Geological Survey offices Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com BGS Central Enquiries Desk Tel 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference collection of BGS publications, including maps, for consultation. email [email protected] We publish an annual catalogue of our maps and other publications; this catalogue is available online or from any of the Environmental Science Centre, Keyworth, Nottingham BGS shops. 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Natural History Museum, Cromwell Road, London SW7 5BD Tel 020 7589 4090 Fax 020 7584 8270 Tel 020 7942 5344/45 email [email protected] Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff CF15 7NE Tel 029 2052 1962 Fax 029 2052 1963 Maclean Building, Crowmarsh Gifford, Wallingford OX10 8BB Tel 01491 838800 Fax 01491 692345 Geological Survey of Northern Ireland, Colby House, Stranmillis Court, Belfast BT9 5BF Tel 028 9038 8462 Fax 028 9038 8461 www.bgs.ac.uk/gsni/ Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon SN2 1EU Tel 01793 411500 Fax 01793 411501 www.nerc.ac.uk Website www.bgs.ac.uk Shop online at www.geologyshop.com Foreword This report is the published product of a study by the British Geological Survey (BGS) illustrating the potential for the use of area cartograms to present geological science information. The project involved establishing an overview of all the types of cartogram used; noting the types of data used in their creation and identifying similar sources of data that may prove appropriate for use in cartograms. Test examples were created and presented along with an evaluation as to their effectiveness and efficiency in communicating spatially orientated datasets. Acknowledgements In addition to the BGS staff acknowledged assistance has been received at all stages of the study. In addition to the collection of data, many individuals have freely given their advice, and provided the local knowledge. Key staff helped to review draft chapters of this report. Of the many individuals who have contributed to the project we would particularly like to thank the following: Richard A Shaw Gerry Wildman Matt Harrison Russell Lawley Wayne Shelley Emma Bee Ian Longhurst The authors would like to thank: Professor Danny Dorling (University of Sheffield) Dr Benjamin D Hennig (University of Sheffield) i Contents Foreword ......................................................................................................................................... i Acknowledgements ......................................................................................................................... i Contents .......................................................................................................................................... ii Summary ....................................................................................................................................... iv 1 Introduction ............................................................................................................................ 1 2 Cartograms ............................................................................................................................. 2 2.1 Distance Cartograms ....................................................................................................... 2 2.2 Area Cartograms ............................................................................................................. 2 2.3 Discussion ....................................................................................................................... 5 2.4 Cartogram Criteria .......................................................................................................... 6 3 Investigations .......................................................................................................................... 7 3.1 World Mineral Production .............................................................................................. 7 3.2 iGeology ....................................................................................................................... 10 4 Results ................................................................................................................................... 14 4.1 World Mineral Production Cartogram .......................................................................... 15 4.2 iGeology App Use Cartogram ...................................................................................... 16 4.3 An Evaluation ............................................................................................................... 17 5 Conclusions ........................................................................................................................... 19 Appendix 1 ................................................................................................................................... 21 Glossary ........................................................................................................................................ 22 References .................................................................................................................................... 23 FIGURES Figure 1: The 2010 general election results. The choropleth map (left) illustrates a clear visual bias in favour of blue, but once the population density equalizing algorithm is applied to each region it becomes clear how the elections in 2010 resulted in a hung parliament. .......... 1 Figure 2: Choropleth map (left) showing the 2008 US election results compared to a contiguous cartogram (right) presenting the same data (Gastner, et al., 2005). ......................................... 3 Figure 3: Two examples of non-contiguous cartograms showing differential weightings for each polygon area (Keim, et al., 2005). ............................................................................................ 4 Figure 4: Illustrating the linking method between the choropleth map and the circular cartogram. Reproduced with author's permission from ‘Maps of the Census: a rough guide’ (Dykes & Unwin, 1998). ........................................................................................................................... 5 Figure 5: A rectangular cartogram (a) showing false topological relationships between Netherlands (NL) and Luxembourg (LU), when in reality these countries do not border each ii other. An alternative would be to allow for abstract (non rectangular) shapes e.g. Hungary (HU) (based on Speckmann, 2006). ......................................................................................... 5 Figure 6: Effective readability – base map extremes in areal unit type and scale. ......................... 7 Figure 7: Choropleth map showing state gold production (2010). ................................................. 9 Figure 8: Choropleth map showing state gold production and political stability (2010). ............. 10 Figure 9: Choropleth map showing iGeology app activation throughout Great Britain between September 2010 – November 2011. ......................................................................................