Why are my co-ordinate axis specifications distorting my image?

Question

I am trying to plot some markers on a to-scale map but when I try to add an axis to my graph corresponding to the coordinates of the map I have used as the background the image distorts. This should have the correct axis ratio:

This aspect ratio but with the axes as specified above.

Answer 1

The geographical coordinates shown on your plot, (1.92S, 52.45E), point to a hot & wet stretch of the Indian Ocean.

On the contrary, if one switches latitude and longitude, the point (1.92W, 52.45N) is in the campus of The University of Birmingham, midway the School of Law and the School of Psychology.

Is it possible that you have made a mistake, exchanging the roles of latitude and longitude?

If this were the case, when plotting remember to fix the aspect ratio: roughly speaking (Earth is almost an ellipsoid, but definitely not a sphere) 0.001⁰ in N-S direction is 111.11 m on ground (always!), while 0.001⁰ in E-W direction, at Birmingham, is just 67.72 m on the ground.

In other words,

from math import cos, pi
...
ax.set_aspect(1/cos(52.45*pi/180))
...

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Footnote

Using ax.set_aspect(1/cos(latitude*pi/180)) is a poor man's map projection that works well until the sides of the mapped area are in the order of km's.

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Addendum

The sides of the two subplots' frames may not be perfectly the same, but I had to guess a reasonable approximation to the pixel size of the image...

import matplotlib.pyplot as plt
import numpy as np

map  = np.random.rand(720, 900)
map += np.random.rand(720, 900)

fig, (no_extent, extent) = plt.subplots(2, figsize=(6,8))
no_extent.imshow(map)
extent.imshow(map, extent=(-1.93933, -1.92384, 52.44757, 52.45508))
extent.set_aspect(1/np.cos(52.45*np.pi/180))
plt.show()