The world is a globe so how can that be accurately represented on a two dimensional surface, when a map is printed on to a poster or in a book?
If you think of the web of lines on a globe that is the grid of latitude and longitude, peeling them off a globe and sticking them on to a flat surface without altering their position or bearing to each other is actually impossible.
In fact, only the distance between two points OR the bearing, which is the direction of one point in relation to another, can be retained and accurately depicted on a map.
There are a number of ways that maps can be drawn to represent the world, each of which is based on a specific mathematical function defining the relationship of points on the map to each other.
The most common map is called the Mercator projection largely because it results in a rectangular which is suitable for presentation in a book or as a world map poster.