mapping people cartograms of ireland martin charlton ncg@nuim.ie ncg@nuim.ie
Post on 17-Dec-2015
232 Views
Preview:
TRANSCRIPT
Mapping PeopleCartograms of Ireland
Mapping PeopleCartograms of Ireland
Martin CharltonMartin Charlton
ncg@nuim.iehttp://ncg.nuim.ie
ncg@nuim.iehttp://ncg.nuim.ie
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 http://www-personal.umich.edu/~mejn/election/
• 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
Changing Population
• We can use the county populations from previous Censuses to examine the effects of population change
• 1841• 1926• 1961 - 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
Population 1841-2002
0
1000000
2000000
3000000
4000000
5000000
6000000
7000000
1841 1851 1861 1871 1881 1891 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991
Date
Po
pu
lati
on
Population by County 1841-2002
0
200000
400000
600000
800000
1000000
1200000
1841 1851 1861 1871 1881 1891 1901 1911 1926 1936 1946 1951 1956 1961 1966 1971 1979 1981 1986 1991 1996 2002
Date
Po
pu
lati
on
Carlow
Cavan
Clare
Cork
Donegal
Dublin
Galw ay
Kerry
Kildare
Kilkenny
Laois
Leitrim
Limerick
Longford
Louth
Mayo
Meath
Monaghan
Offaly
Roscommon
Sligo
Tipperary N.R.
Tipperary S.R.
Waterford
Westmeath
Wexford
Wicklow
Comparison
• (a) 1926 – after Independence• (b) 1961 – population starts
increasing• (c) 2002 – present day
top related