How to make a huge overview of my minecraft project?

I think he is using Shaders mod! It is a very well known mod and you can get many different shader packs! Though it is very heavy as in my PC used to run Minecraft on 500 fps and when I got shaders it went down to 50! You can download it from many different locations. I prefer the links in the description of the youtubers Deadlox or Bodil40! Plus he probably just removed clouds in settings made render distance far and he was done!

There are several ways to achieve a massive overview such as that. Shaders mod was already mentioned but if you play on a server a dynmap also works quite well, unfortunately if the server doesn't have dynmap (they are quite RAM heavy) then you are out of luck.