A paired down method for figuring out the size of a continent inspired by the game Civilization III. This is borrowed almost verbatim from "Learn to Program 2.0" by Chris Pine. It just contains a small addition that prevents the program from crashing when counting 'tiles' that are at the 'edge of the world'.

ContinentSize.rb

# Method from Chris Pine for figuring out 
# continent size in Civilization III 
# with added return conditional for spots at the 'edge of the earth'



M = 'land'
o = 'water'
world = [[M,o,o,o,o,o,o,o,o,o,o],
[M,o,o,o,M,M,o,o,o,o,o],
[M,o,o,o,o,o,o,o,M,M,o],
[M,M,M,M,o,o,o,o,o,M,o],
[o,o,o,M,o,M,M,o,o,o,o],
[o,o,o,o,M,M,M,M,o,o,o],
[o,o,o,M,M,M,M,M,M,M,M],
[o,o,o,M,M,o,M,M,M,o,o],
[o,o,o,o,o,o,M,M,o,o,o],
[o,M,o,o,o,M,o,o,o,o,o],
[o,o,o,o,M,M,o,o,o,o,o]]

def continent_size world, x, y
  
  # Either it's water or we already
  # counted it, but either way, we don't
  # want to count it now.

  if world[x][y] != 'land'
    return 0
  end

  # My addition (at Chris Pine's suggestion) for inclduing locations
  # At the edge of the world without having the program crash 

  if x > 9 || x < 0 || y > 9 || y < 0 
    return 1
  end 

  # So first we count this tile...

  size = 1
  world[x][y] = 'counted land'

  # ...then we count all of the
  # neighboring eight tiles (and,
  # of course, their neighbors by
  # way of the recursion).

  size = size + continent_size(world, x-1, y-1)
  size = size + continent_size(world, x , y-1)
  size = size + continent_size(world, x+1, y-1)
  size = size + continent_size(world, x-1, y )
  size = size + continent_size(world, x+1, y )
  size = size + continent_size(world, x-1, y+1)
  size = size + continent_size(world, x , y+1)
  size = size + continent_size(world, x+1, y+1)

  size

end

puts continent_size(world, 5, 5) #32 given the current configuration of my world array