Geovisualising Land Ownership in Scotland

This blog post represents the first in a new series of GeoGeo's commentary on Scotland, as we add our geospatial skills to the important issues affecting the nation.  As always, we'll emphasise the use of free and open source software to process, analyse and visualise any and all available datasets relating to these issues, whilst pointing out some of the underlying policy landscapes that impact heavily on our ability to do so.  This week, we take a stab at visualising the true extent of land ownership in Scotland.

After much coverage already this month, the issue of land ownership has raised a lot of questions about Scotland's geography, and public understanding of it. Andy Wightman provided a brilliant article as Lateral North's infographic accentuated the statistics. The numbers are staggering, perhaps difficult to fathom and begs the question of how (and why) we have remained largely unaware of the situation.  

Citizens mapping raises the question: how many of us truly understand the geography of Scotland? Could it be that our majority of urbanised residents have simply 'forgotten' about the vast beauty that is the Bonnieland? In an age where our geographies often stop short beyond the place where we work, sleep and (often digitally) socialise; perhaps we have ourselves to blame, in part, for lacking knowledge on how far rich landowners dominate the rural landscape. Could you, for example, list our largest islands in order of size? Could you even name the largest?  Try to answer that before you look at our geovisual comparison below!

Whilst there are now calls for reform, as well as an argument for a land value tax replacing income tax, the issue of our geographic illiteracy continues to underline the larger issue that we have here in 21st Century Scotland...that of openness, transparency and accountability. If all land ownership (geo)data was made open, somebody (probably us geo-geeks) would have already mapped and visualised it. Sadly, with much of Scotland's most advanced mapping datasets tied to a commercial licence, many wholehearted attempts to heighten our knowledge have fallen short despite the admirable endeavours of

So who owns Scotland?  Whilst we are still shy on exact spatial data, Steven Kay takes Scotland's statistics on land ownership one step further to geovisualise (below) what we do know.  

The lack of spatial data available on land ownership in Scotland is worrying.  In May 2014, there were ambitious plans laid out to help map Scottish land ownership and we very much look forward to the results of this Government-based initiative. However, as the saying goes: if you want something done right, do it together.  OpenStreetMap represents a truly open and transparent way of mapping land ownership. The question is whether we should have to wait ten years for the Government's multi-million pound map when we can collectively start now and show the nation that prove right once again Tobler's First Law of Geography: that we know most about what's closest to us....

Here Comes the (Geo)Science Bit - Steven Kay Explains

The challenge in making the land ownership map (above) was to find a way to select a percentage of Scotland's area. I've dubbed the technique 'wildfire spreading', as a metaphor for how it works.  Imagine a fire starts in a single area. The next turn, the fire spreads to its neighbours. The following turn, it spreads to its neighbours' neighbours, and so on. Eventually the fire will ripple out across the whole of the mainland. The fire won't jump across water, so the Islands are safe... for now!
To colourise a portion of the map, I start a virtual fire in a corner. For the Public sector, I chose John O' Groats. We keep track of the total area which has burnt as the fire spreads. When the running total area reaches the target, we stop and record the list of areas which were 'burnt'. These areas are then merged into a solid chunk (buffer & dissolve in QGIS).  The total area won't be exact. By carefully choosing how we divide Scotland, the error can be kept to much less than 1%.  I also minimised errors by getting the fire to spread from an area to its neighbours in increasing order of size. This helps to reduce the number of holes caused by enclaves.. they go on fire first.  There are various ways to divide Scotland into areas. I tried a regular grid, SIMD area polygons, and postcode catchment areas. I chose the latter as it was the most accurate. It also looked more 'organic'. The grid was equally accurate, but looked blocky.

The outline of Scotland was derived from SIMD (Scottish Index of Multiple Deprivation) data from the Scottish Government.
Postcode catchment boundaries were derived from OS Open Code Point, Crown Copyright and Database Rights 2014.

Free & Open Source Tools used

  • SAGA GIS - generating voronoi tesselation from OS postcodes, clipping it to outline of Scotland
  • Postgres / PostGIS - database, finding which areas are neighbours, cleaning geometry from SAGA, calculating areas
  • shp2pgsql-gui - getting area shapefiles into Postgres
  • Python - wildfire spreading script
  • QGIS - cartography