Why is the less the coverage of the territory, the less distortion on the map?

Due to the fact that the map has a limited area, depending on the area of the surface displayed on it, there is a change in the scale of the map itself.
So, in the case of the surface of the Earth, the area of which is 1 square kilometer, on the surface of the map, you can display in more detail all objects that exist in reality.
In the event that an area equal to 100 square kilometers is displayed on a map of the same size, most small objects will not be possible to indicate.