Alabasta is as big as Antarctica so it’s not a small continent
Here is a complete map of Alabasta
You can see the entire island you can also see the river. This river was stated by Vivi to be 50km wide
If we use to pixel lines into the first scan, 50km=2px, therefore 193.6 pixels is equal to (193.6×50)÷2= 4840km long. To find the circular surface area of this island we can use area of a circle= pie×radius^2.
Our radius=Diameter/2=4840/2=2420km.
Therefore the area of Alabasta=3.142×2420^2=18,400,808.8km squared. Meaning Alabasta is more than double surface area than Russia.