Currently Online 
I did a quick estimation, that can be quite off because of a few assumptions I made. But I think it is close enough.
So I traced a path (red line) found in Figure 1 below, the link to the video is in this figure. I "counted" the seconds it took for her to walk this path, subtracting any seconds she stopped to attack enemies. I then used that length to estimate a radius for the area (which is approximately circular.)
I used the average jogging speed of an adult, taking a lower and upper limit, and using the mean with some uncertainty. The time it took her to walk the path was 35 seconds +/- 5 seconds and that gives about 70 - 105 meters for the length of the path. The radius of the whole area then is something like 4.5 times that (estimation based off two different radii estimates). This gives a radius of something like 315 meters to 472.5 meters for the plateau. I then took the average of that to calculate the area of the this whole plateau. I got approximately 580,000 m^2( or .58 km^2. )
Figure 1
Now I approximate how many of these regions fit inside the entire world map.
Figure 2
I get about 60-70, including the ocean space. So if we multiply 65 by .58 sq-km, we get approximately 37.7 sq-km. I also took notice of my uncertainties and using propagation formulae (https://en.wikipedia.org/wiki/Propagation_of_uncertainty ) I recieve a final uncertainty of +/- 6.5 sq-km.
This seems to match the twelve-times Twilight Princess estimate given by Nintendo. And it puts the map at about the size of Skyrim.
Although with how vertical this game is, it definitely feels bigger than that.
