The map shows the contours of the territories of large empires and countries. 
The measurement of their "continuous and contiguous linear extension" is shown, as Professor Durántez Prados clarifies in the following comments on the size of empires:
"It has also been written very repeatedly that the Mongol [Empire] was the largest contiguous empire, the largest continuous territorial bloc, by referring to the space between the Korean peninsula and the European Hungary as a single political unit. However, if we look at the map of the Spanish Empire in 1783, after the reiteration and reconfirmation of the acts of sovereignty over Alaska of the Crown of Spain in the last third of the 18th century, we will clearly see that its imperial area then extended between Tierra del Fuego at the end of America, opposite Antarctica, and the Alaskan lands adjoining the northern part of the Arctic Ocean: that is, practically the largest possible contiguous, linearly, territory on planet Earth. Then, from this perspective, the Hispanic Empire was undoubtedly the empire with the greatest continuous and contiguous linear extension of History.

Durántez Prados, Frigdiano Álvaro, Iberofonía y paniberismo (2018), p.108
Own work
Nagihuin