Then, I cut off all the islands I need and edit color tone of those islands to let them consistent to game's style. Next, according to the size of each islands, I assign different values to those lands. There's some trick when I assign values to them: the numbers are not generally multiple of each other and they are not strictly following the sizes of islands. That is part of lies by host(us) in game. Then, I photoshopped some sea textures and used it as background.