Monday, 1 June 2009

Finding the Centre of Jersey

I saw the centre stone of Jersey today, supposedly in the Geographical centre. I am suspicious as to whether it really is the centre of the Island, geographically, as there are no indications as to how it was calculated. It is at  the side of the road on La Rue des Servais . Lat / Long:      049º 13' 18"N / 002º 06' 57"W  OS Grid Ref:     645527
When one looks around the world, the first place I found was:

The Geographical Center of the United States: Latitude 39 degrees 50 minutes     Longitude 98 degrees 35 minute NE 1/4 - SE 1/4 0 S32 0 T2S - R11W (1)

So how did they calculate it? They do provide details.

With an irregular shape, I would have thought that the best way to find the "centre" is to take that as the centre of gravity of a flat surface of the same height (so that mountains etc are excluded) that follows the same contours  in two dimensions as the geographical actual area to be considered. The advantage of that method is that you can work from an accurate but scaled down model. This is in fact the method used by the U.S. Geologists in determining the centre. The North Dakota website makes this clear:
If one looks at the North Dakota Government website you will find they state "The U.S. Geological Survey does not recognize the geographic center of North America (or that of the 50 States or the conterminous United States) as exact locations. The reason for this is that there is no generally accepted definition of a geographic center and no reliable way of determining it. Consequently there are probably as many geographic centers of a given area as there are definitions. Both Douglas (1930) and the U.S Geological Survey define the geographic center of an area as "…that point on which the surface of the area would balance if it were a plane of uniform thickness,…" This point of balance is the area's center of gravity. The U.S. Geological Survey's published coordinates for the geographic center of North America are based on this definition.(2)

The same technicque has been used for Europe, but with all shapes, it all depends upon where you draw the boundaries as to what constitutes Europe, which is difficult as the geographical boundaries are also related to shifting political boundaries - although, generally speaking, not as broadly defined as the Eurovision song contest!

The location of the geographical centre of Europe depends on the definition of the borders of Europe, mainly whether remote islands are included to define the extreme points of Europe, and on the method of calculating the final result. Thus, several places claim to host this hypothetical centre.(3)

But the method is the same -  the centre of gravity of the shape of Europe, as a two dimensional plane surface.

After a re-estimation of the boundaries of the continent of Europe in 1989, Jean-George Affholder, a scientist at the Institut Géographique National (French National Geographic Institute) determined that the Geographic Centre of Europe is located at 54°54′N 25°19′E / 54.9°N 25.317°E / 54.9; 25.317 (Purnuškės (centre of gravity)).[2] The method used for calculating this point was that of the centre of gravity of the geometrical figure of Europe. (4)

This has not always been the case. One calculation used "extreme points" to determine where the centre lay, and came up with a surprising conclusion. This is a "distance of points" method, and as points chosen are arbitrary, it is very difficult to argue a good case for any one set over others. If Jersey's used this method, points on West and East, and North and South could be chosen, and the centre would be where each crossed. Or points could be taken on each farthest extremity. It is an extremely subjective method. This is what some of the calculators came up with Europe:
Based on distance calculations to the extreme points of Europe (Franz Josef Land in the Northeast, the border between the Russian Federation and the states of Georgia and Azerbaijan at the Caspian Sea in the Southeast, Crete in the South and the Azores in the Southwest) the centre of Europe will surprisingly be found in Southern Norway near 60°00′N 07°30′E / 60°N 7.5°E / 60; 7.5 in the Telemark region.(5)
So the best way is clearly the centre of gravity method. But at low or high tide? Where are the boundaries of Jersey - are they inshore from the highest tide, or from the lowest? And - taking either of these methods - how has this altered with the land reclamations in St Helier? Is that significant or not?

It would, I think, be an interesting project for a local school.

In the meantime, if you want to visit the site, and see a stone, which while not perhaps the centre of the Island, is probably neolithic, and has an interesting cup mark on it, it can be found on Perry's Guide:   p 30 C2, and can be seen online at the excellent Prehistoric Jersey site:


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