To give a little info on the significance of a datum, there is a 300 meter difference in x,y coordinates between the NAD27 and NAD83 datums. More on the Geod - the definition of the shape of the earth is the field of Geodesy. In theory, the geoid runs through sea level and is a representation of the gravity field of the earth. Far more accurate than mere datum measurements. Note that area and angle are mutually exclusive.
Great circles are straight lines.
Often viewed with the pole at the center. Compromise Nothing is preserved, but nothing is super distorted. Robinson Note that both distance and azimuth preserved projections only apply to or from the center of the map projection. Also, they usually only show 1 hemisphere or half the earth. All commercial rights reserved.