Plot coordinates of boroughs of london doesnt seem to be right

Hi there,

I am plotting on a series of latitude/longditude points based on the boroughs of London. I have got a map of London and tried to scale it to the correct size. My points seem wrongly plotted in the y direction, almost as if they are squashed. In the x direction it all seems fine. Is this to do with the curvature of the earth affecting how the points are plotted against a flat map?

Any help at all is appreciated and needed quite quickly! Argh!

Thanks!!!

George

Replies to This Discussion

Permalink Reply by David Rutten on December 8, 2012 at 7:14am

We're going to need to see some data and algorithms. I don't know what's going wrong until I can see what's going on.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by g on December 8, 2012 at 7:36am

Sorry. It is a simple xyz plot of coordinates for each borough of london. The plotted data is in the right place but when compared to a 2d map of london it is way more squashed than it should be. It cant be the map im using as ive tried lots of different ones and that is just the shape of london... If i plot the same coordinates in google maps it does it correctly but not here...

Thanks!

Permalink Reply by David Rutten on December 8, 2012 at 8:41am

Well yes, lat-lon coordinates do contract as you move away from the equator. By the time you reach the poles, the contraction is infinite, which is why the poles are considered to be singularities in a lat-lon mapping. There is no way to project a shape that exists on a sphere onto a 2D plane without some deformation. There's two approaches I see that could make sense:

Reconstruct your geometry in 3D space, i.e. on a sphere. Then project it onto a plane that fits the point-set well.
Add an adjustment scaling factor for the latitude coordinates that takes into account the shortening that happens at your average latitude.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by David Rutten on December 8, 2012 at 8:43am

Ah, a third one. You could also subtract the average latitude from all your latitudes, effectively placing London on the equator where the deformation is smallest.

David Rutten

david@mcneel.com

Poprad, Slovakia

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