Quick and dirty world building...

Is the blob landmass or ocean? We need a reasonable target hydrographic ratio and the land ratio, to use in finding a random world map filling procedure.

One way is to choose a target number, the lesser of two d% rolls. If less than, it's landmass, if greeter, ocean. Landmass is less likely and trends smaller, but we could still see vast continents or tiny oceans 

50 and 41, so a 41% chance of landmass. 36, a 36 m. km^2 continent half again the size of North America.