A Day and Night World Map shows which parts of the Earth are in daylight and which are in night at a given instant. At one side of the Daytime line they are in daylight and at the other side they are in twilight.
The shape of the day and night areas are different at the different days of the year.
What I would like to know is:
How is the calculation of the shape of the areas in a Day and Night World Map done?
What is the curve that describes the Daytime line in a Day and Night World Map?
I suspect it has to do with the projection of a great circle on an Equirectangular projection of the world map... but I would like to know if this is correct or not.