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Author Topic: Where is the geographic centre of South Africa?  (Read 12377 times)

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Offline RobC

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Re: Where is the geographic centre of South Africa?
« Reply #80 on: September 16, 2011, 09:42:14 am »
That's why I suggested that the midway between W+E and N+S appears to be the simplest method.
But we need the TRUE Longitude and latitude values for the W, E, N + S points.
I have tried using Mapsource and Google Earth, but I arrive at a midpoint NE of Barkly West,
near the farm homestead Kilmoray.
 ???
That is near my suggested point too.
I went in on Google maps and plotted points for NSWE vectors and then calculated the difference between the lat. long. divided by 2 then added that to one of lesser co ordinates and arrived at my rough RV. But as you say a 1/2 degree in any direction is quite a difference when plotted.
Do you have the co ordinates for your point?
Lets get as many as possible and then divide those results too! :mwink:
 

Offline RobC

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Re: Where is the geographic centre of South Africa?
« Reply #81 on: September 16, 2011, 09:43:12 am »
If there is more than 1 centre point, we could plot those (which will be only a few) and then get to the centre of the centre  :biggrin:


and plot the ride to visit them all! :mwink:
 

Offline Fudmucker

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Re: Where is the geographic centre of South Africa?
« Reply #82 on: September 16, 2011, 04:51:23 pm »
That is near my suggested point too.
I went in on Google maps and plotted points for NSWE vectors and then calculated the difference between the lat. long. divided by 2 then added that to one of lesser co ordinates and arrived at my rough RV. But as you say a 1/2 degree in any direction is quite a difference when plotted.
Do you have the co ordinates for your point?
Lets get as many as possible and then divide those results too! :mwink:

I did exactly the same and arrived at the point:

Latitude: -28.47991493 Longitude : 24.67269332
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Offline RobC

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Re: Where is the geographic centre of South Africa?
« Reply #83 on: September 16, 2011, 05:23:06 pm »
That is near my suggested point too.
I went in on Google maps and plotted points for NSWE vectors and then calculated the difference between the lat. long. divided by 2 then added that to one of lesser co ordinates and arrived at my rough RV. But as you say a 1/2 degree in any direction is quite a difference when plotted.
Do you have the co ordinates for your point?
Lets get as many as possible and then divide those results too! :mwink:

I did exactly the same and arrived at the point:

Latitude: -28.47991493 Longitude : 24.67269332
also good... just west of my first picture (the dam and sheep) :thumleft:
 

Offline tok-tokkie

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Re: Where is the geographic centre of South Africa?
« Reply #84 on: September 17, 2011, 10:16:34 am »
That is near my suggested point too.
I went in on Google maps and plotted points for NSWE vectors and then calculated the difference between the lat. long. divided by 2 then added that to one of lesser co ordinates and arrived at my rough RV. But as you say a 1/2 degree in any direction is quite a difference when plotted.
Do you have the co ordinates for your point?
Lets get as many as possible and then divide those results too! :mwink:

I did exactly the same and arrived at the point:

Latitude: -28.47991493 Longitude : 24.67269332
If you did hat on an L shaped country like Namibia your 'center' point will be very far to one side which is why I think the center of gravity method is much better.
 

Offline Sláinte Mhaith

Re: Where is the geographic centre of South Africa?
« Reply #85 on: September 17, 2011, 10:57:44 am »
That is near my suggested point too.
I went in on Google maps and plotted points for NSWE vectors and then calculated the difference between the lat. long. divided by 2 then added that to one of lesser co ordinates and arrived at my rough RV. But as you say a 1/2 degree in any direction is quite a difference when plotted.
Do you have the co ordinates for your point?
Lets get as many as possible and then divide those results too! :mwink:

I did exactly the same and arrived at the point:

Latitude: -28.47991493 Longitude : 24.67269332
If you did hat on an L shaped country like Namibia your 'center' point will be very far to one side which is why I think the center of gravity method is much better.

+1 Those methods can't be correct.
 

Offline Sláinte Mhaith

Re: Where is the geographic centre of South Africa?
« Reply #86 on: September 17, 2011, 10:58:44 am »
http://en.wikipedia.org/wiki/Geographical_centre

In geography, the centroid of the two-dimensional shape of region of the Earth's surface is often known as its geographical centre. There has long been debate over the methods of calculation of the geographical centres of various countries and regions, such as whether to include offshore islands, and in that case, if the islands should be moved towards the mainland, making it possible to build a connected 2D model of the country and identify the geographical centre as the centre of gravity (equilibrium point) using a needle. An alternative to defining the geographical centre as the centroid is to define it as the point farthest from the boundary of the country (either the sea, or, in the case of constituent countries, a land border). These methods give quite different answers.
 

Offline White Rhino

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Re: Where is the geographic centre of South Africa?
« Reply #87 on: September 18, 2011, 05:35:39 am »
This is what I calculate with some pictures to illustrate my sources....

Western Point  28°37'52.00"S  16°27'20.00"E
Eastern Point  26°51'27.52"S  32°53'28.86"E
Norther Point  22° 7'30.01"S  29°39'25.80"E
Southern Point  34°50'0.00"S  20° 0'0.00"E

Centre point  28°28'45.00"S  24°40'23.30"E

Distance from Kimberly 28 kms NNW (343.68°)

The centre point is 12km from the N12 and 5kms after crossing the Vaal River.

Looks like a few quarries around with some farming in the general area.  >:D





« Last Edit: September 23, 2011, 05:10:20 am by White Rhino »
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Offline Fudmucker

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Re: Where is the geographic centre of South Africa?
« Reply #88 on: September 19, 2011, 06:46:20 pm »
Pretty close to where I got, but you're a teeny bit East.

Wikipedia gives Cape Agulhas as 34 50 00S and 20 00 09.15 E
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Offline Sláinte Mhaith

Re: Where is the geographic centre of South Africa?
« Reply #89 on: September 19, 2011, 08:24:35 pm »
http://en.wikipedia.org/wiki/Geographical_centre
In geography, the centroid of the two-dimensional shape of region of the Earth's surface is often known as its geographical centre.

Didn't finish my 5c the other day:


Geographical centre ------> Centroid of 2 dimensional shape

Centroid -------->




This is not a north/south and east west method. Therefore I agree with kaalkoejawel and Tok Tokkie.



For an odd shape this method seems practical:

Plumb line method

The centroid of a uniform two-dimensional lamina, such as (a) below, may be determined, experimentally, by using a plumbline and a pin to find the center of mass of a thin body of uniform density having the same shape. The body is held by the pin inserted at a point near the body's perimeter, in such a way that it can freely rotate around the pin; and the plumb line is dropped from the pin (b). The position of the plumbline is traced on the body. The experiment is repeated with the pin inserted at a different point of the object. The intersection of the two lines is the centroid of the figure (c).

 

Offline Fudmucker

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Re: Where is the geographic centre of South Africa?
« Reply #90 on: September 19, 2011, 08:49:13 pm »
 ::) Yup, that's the other way that it is done.
Anyone care to cut up a big map and hang it up from 2 or 3 points?
Remember to cut Lesotho out first too.
Having done so, anyone have an idea how we would find the exact coordinates of the crossed lines... ?  ::)
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Offline Sláinte Mhaith

Re: Where is the geographic centre of South Africa?
« Reply #91 on: September 19, 2011, 09:20:47 pm »
::) Yup, that's the other way that it is done.
Anyone care to cut up a big map and hang it up from 2 or 3 points?
Remember to cut Lesotho out first too.
Having done so, anyone have an idea how we would find the exact coordinates of the crossed lines... ?  ::)

Kaalkoejawel has done it electronically, although his map (on page 2) is not very accurate.
His point seems to be just east of Kimberley although it is difficult to transpose.
If you really want to be accurate you should probably also include the islands.
« Last Edit: September 19, 2011, 09:21:17 pm by Sláinte Mhaith »
 

Offline White Rhino

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Re: Where is the geographic centre of South Africa?
« Reply #92 on: September 20, 2011, 02:29:12 am »
Pretty close to where I got, but you're a teeny bit East.

Wikipedia gives Cape Agulhas as 34 50 00S and 20 00 09.15 E

FM Isn't the important coord the Southern one - 34 50 00S  - the East point should (20 00 09.15 E) be ignored as the Far Eastern point is the important one ?
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Offline Fudmucker

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Re: Where is the geographic centre of South Africa?
« Reply #93 on: September 20, 2011, 06:04:42 pm »
Pretty close to where I got, but you're a teeny bit East.

Wikipedia gives Cape Agulhas as 34 50 00S and 20 00 09.15 E

FM Isn't the important coord the Southern one - 34 50 00S  - the East point should (20 00 09.15 E) be ignored as the Far Eastern point is the important one ?

 :eek7: You're right of course!

(FM you dumb clutz!)  :-[
« Last Edit: September 20, 2011, 06:07:46 pm by Fudmucker »
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Offline Tommy Transalp

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Re: Where is the geographic centre of South Africa?
« Reply #94 on: September 20, 2011, 07:25:12 pm »
With GPS co-ords... Let's organise a national bash there sometime (wherever that may be!)
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Offline Pistonpete

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Re: Where is the geographic centre of South Africa?
« Reply #95 on: September 20, 2011, 08:24:12 pm »
and the final co-ords are?  :)
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Offline White Rhino

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Re: Where is the geographic centre of South Africa?
« Reply #96 on: September 21, 2011, 06:25:48 am »
In GPS lingo I make the Centre point  25 Y0031989 X3151554

In Long & Lat - 28°28'45.00"S  24°40'23.30"E
« Last Edit: September 21, 2011, 06:26:43 am by White Rhino »
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Offline The Rock

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Re: Where is the geographic centre of South Africa?
« Reply #97 on: September 21, 2011, 08:09:05 am »

Plumb line method

The centroid of a uniform two-dimensional lamina, such as (a) below, may be determined, experimentally, by using a plumbline and a pin to find the center of mass of a thin body of uniform density having the same shape. The body is held by the pin inserted at a point near the body's perimeter, in such a way that it can freely rotate around the pin; and the plumb line is dropped from the pin (b). The position of the plumbline is traced on the body. The experiment is repeated with the pin inserted at a different point of the object. The intersection of the two lines is the centroid of the figure (c).
thats interesting! i didnt know that!

and yes, the map i used is a very rough outline, so it will be a bit off. i couldnt find a more accurate one in dwg format.
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Offline MildDog

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Re: Where is the geographic centre of South Africa?
« Reply #98 on: September 21, 2011, 10:58:00 am »
F**k you okes have made this way complicated.

Just pick a spot somewhere in the middle and ride there :)
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Offline RobC

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Re: Where is the geographic centre of South Africa?
« Reply #99 on: September 21, 2011, 11:11:48 am »
F**k you okes have made this way complicated.

Just pick a spot somewhere in the middle and ride there :)
My suggestion is Barkly West... find a place to stay and then explore the different points mentioned from there.
AFAIK there are one or two good campsites on the river.
I feel like taking a ride out there this weekend... :deal: