What two major decisions must a cartographer make before making a map?

Answer

scale and projection

Explanation.

These are the major fundamental features of of maps. Scale is referred as to how map units relate to real world units. Scale is used to measure how much the features of the world are reduced to fit on a map or still map scale shows the proportion of a given distance on a map to the corresponding distance on the ground in the real world.  

Projection deals with  the methods and challenges around turning a three dimensional earth into two-dimensional map. The graticule on a globe i.e  lines showing parallels of latitude and meridians of longitude for the earth. Graticules can be used to show location in geographic coordinates and are much helpful in forming two dimensional geographic coordinates from three dimension.