Wednesday 3 March 2021

Where's the Centre of Scotland?

A little bit of map trivia today, inspired by a recent exchange on Twitter and also because it served as a useful training exercise for my new training courses. It's also related to a previous blog post from last year on Scotland's 'pole of inaccessibility' (near Braemar, since you ask), as well as other exchanges here and there (exhibit a, exhibit b). Okay, so let's start with a map of Scotland showing a variety of different 'centre' points, and then I'll work through each of them until I decide which I think are the right ones. One conclusion: the 'central' belt might need a new name. Another conclusion? Dollar could launch a whiz-bang marketing strategy that includes the words 'The Centre of Scotland'.

Dalwhinnie? Dollar? 

The answer to the question 'Where's the Centre of Scotland?' does of course depend upon how you define it ('it' being both 'centre' and 'Scotland'). I'll leave the question of marine areas out of this discussion and say that I'm only going to focus on the land area of Scotland - from Shetland in the north, out to St Kilda in the West and to the Mull of Galloway in the South. The most easterly point is also in Shetland.

Let's start with the slightly unusual ones.

This is the centre of Scotland based on Scotland's 'minimum bounding circle'.

Off the coast, near Buckie

What about the centre of Scotland based on the 'minimum bounding box'?

Closest town is Dingwall

How about if you orient the bounding box more naturally, to fit Scotland's shape rather than doing it on a north-south axis?

On land, between Buckie and Keith

Now, these ones so far can make some sense (at a stretch) but they are all large shapes. What if we use a 'convex hull'? This is of course a tighter shape, and should give a different result.

Munlochy - in the middle of the Black Isle

Okay, how about the point furthest from the sea? Well, this is known as the 'pole of inaccessibility' (whether on land or sea) and here it is. You can read all about it - and see pictures of it - in my blog post from last year. For the centre point of the mainland, that's a different calculation but I believe it is near Schiehallion.

Very close to Braemar, in the Cairngorms

Okay, these are all very interesting, but what about the centre of Scotland based on a) landmass and b) population? Okay, here you go.

A little bit south of Dalwhinnie, off the A9

Just outside Dollar

Here are a couple of zoomed-in views of the Dalwhinnie/Trinafour geometric centroid of Scotland and the Dollar population-weighted one.

You can easily see this from the road

I have double-checked this, seems legit

I also did a 60 minute drive time check to see what can reasonably be reached from Dollar within an hour - here's the map of that. The population within the light area in the map below is just over a million, within reach of Dollar.

The million Dollar population question

Here's the first map again, but this time with some place labels on it. I also have a web map version showing just the two most logical centre points (the geometric centroid and the population-weighted one).

The centres of Scotland

Nerd notes: are these calculations correct? I believe so. I have double checked and I did them based on the highest resolution Ordnance Survey data available. I also did them using much lower resolution, generalised data and got almost exactly the same results. Search the web and you'll quickly find the Centre of Scotland Wiki article, which would appear to corroborate the A9 location. 

I couldn't find anything at all online about Scotland's population-weighted centroid - possibly bad at searching - but I did these calculations using two datasets. One was a 1km gridded population dataset of Scotland from 2011. The other was a set of data zone population-weighted centroids from 2019. Both calculations put the location of the population-weighted centroid outside Dollar. It also makes sense when you look at the population distribution of Scotland, as in the travel time map above.

Why do this? I am running a new series of training events on data, maps and analysis so this was a useful training dataset, plus I'm Scottish and was curious about the topic.