https://en.wikipedia.org/wiki/Equire...lar_projection
Look at the Tissot's indicatrix and everything will be known.
If we have some East-West distance X on equator and it is represented by a line of length Y on map, same distance at latitude Z will be represented by line of length Y/cos(Z). So 20 horizontal pixels at 60 degree North is the same distance as 10 pixels at Equator.

Fun fact: at the pole factor 1/cos(Z) runs to infinity and we draw it this way indeed - cause we have a point which has no length represented as a line which has a length.