Our Earth is a 3D planet, hence it was difficult for early Cartographer to put it into a 2D map. In 1569, Gerardus Mercator, a Flemish geographer and cartographer came up with a solution, he designed a map that could be accurately used for navigation but the only drawback that he saw was that his system distorted the size of objects depending on their position relative to the equator.
You might have noticed that some countries look bigger and some looks smaller on 2D map. Mercator Projection is responsible for difference of size of various countries. This is why, landmasses like Antarctica and Greenland appear much larger than their actual size.
Here are some images showing the actual size of various countries. You can also visit thetruesize.com to see the actual size of other countries other than the ones listed below.
US moved down next to Australia looks unbelievably small in size.
Russia on the equator seems giant but actually its not.
In the Arctic Ocean, if Romania was an Island.
Australia is actually far bigger than you think.
If Brazil was in Asia, it would be massive.