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GIS users- could someone please help me find the centroid of a shape on a map?

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I'm doing a little pet project/mini documentary on a local utility project.ย 
I'd love to be able to grab the grid references for the centre of the proposed site.ย 
I've got a rough shape for the site.ย 
The vision is to start filming there and use it as a reference for the future too, almost like a ground zero.ย 
The grid reference provided for the development is wildly off.ย 

Could any GIS users help me with this please?ย 


 
Posted : 11/02/2025 3:00 pm
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Could you get the OS locate app for your phone and walk/cycle over there ?


 
Posted : 11/02/2025 3:11 pm
 Olly
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https://gridreferencefinder.com/ is a good resource for getting OS grids.

You can also load shape files and kmzs etc into ChatGPT and it can handle a surpising amount of basic GIS tasks.

What is the centroid of this polygon, in OSGB

worked for me for a random test polygon.

Bear in mind that a centroid of a site might not be on the site, if its a funny shape . Its just the halfway point betwenen the maximum extents.

You could also look at "point of inaccesability", which is basically furthest distance to and edge in any direction.


 
Posted : 11/02/2025 3:33 pm
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Thanks both!
Currently drawing polygons and creating KMZ files to test.ย 


 
Posted : 11/02/2025 4:12 pm
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In the old days. You cut it out on paper.

Get a knife edge and move it until it balances. Thats one line. Rotate it until it balances again. Those too lines intersecting...

Careful with the scissors, ask a grown up if you need help.

ย 


 
Posted : 11/02/2025 4:24 pm
leffeboy reacted
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Print it on the largest piece of cardboard you can. Poke pins through it and hang it on a plumb line. Draw lines following the plumb line. You'll have a cocked hat at the centroid.


 
Posted : 11/02/2025 4:29 pm
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Or just print two copies on heavy paper. Use balance scales to find where the horizontal and vertical centers of mass are. Slice them in half, then keep slicing small slices off the heavier side and adding them to the lighter side until they balance. That's the center of mass. The intersection of the vertical and horizontal centers of masses should be the centroid.


 
Posted : 11/02/2025 4:43 pm
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Or just print two copies on heavy paper. Use balance scales to find where the horizontal and vertical centers of mass are. Slice them in half, then keep slicing small slices off the heavier side and adding them to the lighter side until they balance. That's the center of mass. The intersection of the vertical and horizontal centers of masses should be the centroid.


 
Posted : 11/02/2025 4:44 pm
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This site is very useful and might avoid you needing to get into GIS plottingย 

https://gridreferencefinder.com


 
Posted : 11/02/2025 6:22 pm
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Just look for the nearest cemetery; the dead centre, innit


 
Posted : 11/02/2025 7:00 pm