Mapping People Cartograms of Ireland Martin Charlton

Outline Cartograms Population Cartogram of Ireland Population Change

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

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

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

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

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

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”

Software Gastner and Newman’s C code is available for download from their website It can be compiled and run on a desktop/laptop PC… … or something more powerful

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

Ireland as we (think we) know it

County Boundaries

… applying the cartogram projection gives us something different…

Changing Population We can use the county populations from previous Censuses to examine the effects of population change

1841

1926

1961

1971

1981

1991

2002

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

1841

1851

1861

1871

1881

1891

1901

1911

1926

1936

1946

1951

1961

1971

1981

1991

2002

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

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