There are many maps that portray the Earth on flat paper. None of them are perfect, though,

because the Earth is a sphere. Flattening out the land and oceans of Earth introduces errors. Two
scientists think they've figured out the best flat map so far. On February 15, they reported a new
map with the Earth flattened into two pancakes. One shows the Northern Hemisphere and the
other the Southern Hemisphere, with the equator running around the edge.
These two pancakes represent the most exact flat map
of Earth ever made, the scientists said. Unlike other
flat maps, the new circular map doesn't downsize or
supersize certain oceans or landmasses. For instance,
many two-dimensional (2D) maps show Greenland as
about the same size as Africa. Actually, Africa is 14
times larger.

What is one issue with the Mercator Projection?

Simple Answer

One issue with the Mercator Projection is that it significantly distorts the size of landmasses, particularly towards the poles.