1. Mapping People Cartograms of Ireland Martin Charlton ncg@nuim.ie http://ncg.nuim.ie ncg@nuim.ie http://ncg.nuim.ie

2. Outline Cartograms Population Cartogram of Ireland Population Change

3. Places not people People tend not to spread themselves uniformly across land areas They tend to live where it’s more convenient to do so (for example: lowland areas, near rivers, near raw materials) They’re also gregarious – live in settlements They don’t usually live in the middle of deserts or tundra

4. Showing people We’re so used to thinking in terms of the physical or political earth that we forget about the social earth. Our maps represent physical or administrative features (roads, trees, rivers, buildings) but not people

5. Showing people… Showing the results of an election or incidence of a disease presents a problem In areas of high population density the physical size of the zones to be mapped is often small Large rural areas with low populations dominate the visual effect and can give us a misleading impression of the underlying spatial pattern

6. People based maps Can we, therefore, come up with a map projection in which the sizes of the zones are in proportion to the number of people than live in them? Yes… they’re known as –Value-by-area maps –Density-equalising maps –Cartograms

7. Creating cartograms In the late 1950s the US geographer Waldo Tobler became interested in the possibilities of using computers to carry out the calculations for cartograms His PhD ‘Map Transformations of Geographic Space’ appeared in 1961

8. Gastner & Newman Recently Michael Gastner and Michael Newman, both physicists, proposed another solution based on diffusion Like Dorling’s method it allows regions to ‘trade their area until a fair distribution is reached’ However it is not tied to an underlying lattice – results don’t look “blocky”

9. Software Gastner and Newman’s C code is available for download from their website http://www-personal.umich.edu/~mejn/election/ It can be compiled and run on a desktop/laptop PC… … or something more powerful

10. Cartogram of Ireland We used Gastner and Newman’s method to produce a density- equalized map of Irish counties The starting point is a list of coordinates for each county boundary in the Irish National Grid system… … and the populations of each county

11. Ireland as we (think we) know it

12. County Boundaries

13. … applying the cartogram projection gives us something different…

14. Changing Population We can use the county populations from previous Censuses to examine the effects of population change 1841 1926 1961 - 2002

15. 1841

16. 1926

17. 1961

18. 1971

19. 1981

20. 1991

21. 2002

22. Population Scaling The previous cartograms show how the segments of the Irish ‘cake’ are redistributed according to the changes in population We can also scale the cartograms so that the total land area is in proportion to the total population in each year

25. 1841

26. 1851

27. 1861

28. 1871

29. 1881

30. 1891

31. 1901

32. 1911

33. 1926

34. 1936

35. 1946

36. 1951

37. 1961

38. 1971

39. 1981

40. 1991

41. 2002

42. Comparison (a) 1926 – after Independence (b) 1961 – population starts increasing (c) 2002 – present day

43. 1926 1951 2002

44. Cartograms Cartograms provide another way of communicating data about people They make us think about people space and not physical space They make us think about the underlying social processes