Overview
Let me give you a brief example of how it works. The world consists of an array (20 x 20) of maps, and in each map, there is an array (20 x 20) of blocks. For further information, I am using C#, and XNA.

Problem
I use serialization to save the whole world but when I do, the file size is at least 170 Mb. Maybe I am doing it wrong, but I do not know why it is such a large file. If you guys could help me by giving me a better way to save data that would be awesome!

Extra
I did make it so it only generates the maps that you go into, and the file size is relatively small. But once the player starts playing the game and starts exploring, the file size will eventually be way too large.

Thank you in advance.