タイルの説明によく使う図（地理院タイル版） ref: http://qiita.com/handygeospatial/items/adbb7a15e3553fab5bd2

file0.rb

for z in 0..2
  for x in 0...(2 ** z)
    for y in 0...(2 ** z)
      next if File.exist?("#{z}_#{x}_#{y}.png")
      `wget -O #{z}_#{x}_#{y}.png http://cyberjapandata.gsi.go.jp/xyz/std/#{z}/#{x}/#{y}.png`
    end
  end
end

for z in 0..2
  files = []
  for y in 0...(2 ** z)
    for x in 0...(2 ** z)
      `convert -font '/System/Library/Fonts/HelveticaNeue.dfont' -pointsize 48 -gravity center -annotate 0 "#{z}/#{x}/#{y}" #{z}_#{x}_#{y}.png with_txt_#{z}_#{x}_#{y}.png`
      files << "with_txt_#{z}_#{x}_#{y}.png"
    end
  end
  `montage #{files.join(' ')} -geometry +#{z+1}+#{z+1} conv_#{z}.png`
end