Map range circles

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MK2wx
Posts: 24
Joined: Sun Jul 16, 2017 10:01 pm

Map range circles

Post by MK2wx » Sat Aug 19, 2017 8:20 am

Hello folks,

I noticed something slightly odd: set map circles to the max of 9, then make the circles 100 nm apart.

Zoom out until you can see the circles entirely. Notice that circles to the south are closer together than those to the north.

I'm sure there must be all sorts of geographic arguments which will be brought forth, but in that case where are there discrepancies involving east west, which would be equally valid presumably?

Perhaps it's just not drawn right?

Anyway, it's odd for certain.
Cheers,
Ian

Datamix
Posts: 51
Joined: Thu Aug 10, 2017 7:36 pm

Re: Map range circles

Post by Datamix » Sat Aug 19, 2017 11:46 am

Do you mean like this?

Image

I never noticed this but it could be because of the curvature of the earth.
VRS: v3 (24-JUN-2018)

MK2wx
Posts: 24
Joined: Sun Jul 16, 2017 10:01 pm

Re: Map range circles

Post by MK2wx » Sat Aug 19, 2017 9:41 pm

Yes, that's it, and thanks for posting the image, I can't do hotlinked images at the moment!

If it is earth curve then the viewing point probably isn't above the site location presumably. That in itself seems a bit odd at first glance.

I'll maybe go play in google earth and see how the accuracy holds up.

It does seem strange.
Cheers,
Ian

agw
Posts: 2105
Joined: Fri Feb 17, 2012 3:20 am

Re: Map range circles

Post by agw » Sun Aug 20, 2017 9:44 pm

It's because the earth is a sphere and Google Maps is showing you a 2D rectangle, so the sphere needs to be projected onto the rectangle. You can read up on the specific projection they're using here:

https://en.wikipedia.org/wiki/Web_Mercator

If you follow the links on there through to the discussion on the Mercator projection then that shows lots of examples of the distortions it introduces.

MK2wx
Posts: 24
Joined: Sun Jul 16, 2017 10:01 pm

Re: Map range circles

Post by MK2wx » Mon Aug 21, 2017 6:53 am

agw wrote:It's because the earth is a sphere and Google Maps is showing you a 2D rectangle, so the sphere needs to be projected onto the rectangle. You can read up on the specific projection they're using here:

https://en.wikipedia.org/wiki/Web_Mercator

If you follow the links on there through to the discussion on the Mercator projection then that shows lots of examples of the distortions it introduces.
Thanks for the clarification, it is most helpful!

While playing in google earth I also noticed that the distances were, as close as makes no odds, still correct.
Cheers,
Ian

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