All projections cause some geometric distortions to the objects that are being projected. Reference globe is a scaled-down representation of earth that is subsequently used for creating projections. Scale factor is a ratio of actual and principal scales. All of the above. It is a good practice to use various projections in one atlas, so the viewer can easier compare different maps.
Conformal projection maintains correctly the relative sizes of projected areas.
Azimuthal projections use conic-shape projection surfaces. Apart from the methodological considerations, the page size and layout of the final publication may affect the choice of projections used. Scale in different points of the map is less accurate as the areas shown become larger. Numeric scale indicators on the map should be well rounded. False northing in UTM equals 10,000 km and is applied in the Northern Hemisphere.