Monday 2 February 2015

Distribution of sheep farming and diary farming in NZ

From sheep farming to dairy farming

New Zealand is world famous for its sheep. However, in recent decades many New Zealand farmers have been converting from sheep to dairy farming. These conversions have been motivated in part by high export prices for dried milk powder and other dairy products. New Zealand sheep numbers peaked in 1982 at 70.3 million and have since declined to 29.6 million.

In 1941 Oliver Duff wrote that the choice of sheep or dairy farming was a  battle of civilisations. From the New Zealand Electronic Text Collection:
"For the history of New Zealand is not so much a struggle between different races of men as between two great families of domestic animals. It is the battle of the sheep and the cows ... if it is not quite the battle of two civilisations, [it] is the battle of two social systems. Sheep make gentlemen and cows unmake them. Sheep leave you with clean hands and clean feet, but cows drag your pride into the mud. Sheep leave you free, cows enslave you. Sheep make you a big farmer, cows make you a small farmer." 
The gentrifying influence of sheep farming seems to be less strong in the 21st Century.

I was interested to see dot density maps of sheep and dairy cows in New Zealand in 1941, which show clearly the dominance of dairy in the west and sheep in the east. Below is an updated map showing the livestock numbers of sheep, beef and dairy cows in 1994 and 2013.

Click image for bigger version
The proliferation of dairy cows in Waikato, Canterbury and Southland is clearly visible as is the nationwide decline in sheep numbers.

How the map was made

Data Sources

Department of Conservation, Public Conservation AreasCC by 3.0 NZ.
LINZ, NZ Exotic ForestsCC by 3.0 NZ
LINZ, NZ Native ForestsCC by 3.0 NZ
LINZ, NZ Lakes, Creative CC by 3.0 NZ
Statistics New Zealand, Regional Authorities 2013 Clipped.
Lucas New Zealand, Land Use Map 1990-2008CC by 3.0 NZ.
Statistics New Zealand, Live Stock Numbers by Regional Council.

Sheep Photograph, Sarah MacMillan, EssjayNZCC BY-NC-SA 2.0
Cow Photograph, Mulla Eshet, Robert Harding World Imagery, Corbis, CC BY-NC-SA 2.0.


Mapping: ArcGIS Desktop 10.2
Masking: Gimp 2.8.6
Final layout and text: Inkscape 0.48


The map is an dasymetric dot density map. White, brown and black points are randomly distributed across the Regional Authority polygons such that their density is proportional to the density of sheep, beef and dairy livestock numbers respectively.

The dot density map is dasymetric because the dots are confined to areas that are classified as pasture in the Land Use Map and excluded from areas classified as National Park, Wilderness Area, Nature Reserve or Conservation park in the Public Conservation Areas.

Dot density maps work best with only one band. If there are multiple bands the drawing order tends to create a visual bias toward the band that is drawn on top. Using transparency creates a washed-out look so, instead, I minimised the bias using an additional  field. I randomly assigned values from 1-3 to the additional field, symbolised the points by Unique Values Many Fields (type field and random field), and used the random value as the drawing order.

A cartographic purist would argue that dot density maps should be created using an equal area projection but the areal distortion of mainland NZ under NZTM is not significant. so I decided to use the familiar projection.

In order to have background images, the very annoying .png transparency bug in ArcGIS forced me to export the map with a blue background and convert this to transparent in external software. I have heard a rumour that this bug is finally fixed in 10.3: I hope so.