Answer:
the center of the earth, the north and south poles, the equator and the Prime Meridian.
Step-by-step explanation:
To obtain a precise latitude, map makers use 4 universal well-known points of reference that make unanimity among the science community, to ensure consensus.
Those reference points are:
1.) the center of the earth: that is used to calculate the radius of the circles and the various angles to draw the latitude lines.
2). the north and south poles: since the latitude lines have to reach them, starting from the Equator.
3.) the equator: that's latitude 0, so it's a pretty important reference point.
4.) the Prime Meridian, as a perpendicular line for the latitude "rings" and other calculations.
And the same reference points are also used to calculate the longitudes as well.