Mini-Maps are an essential GUI element for many types of games; a great help for users’ wayfinding and navigation efforts.
If you’re lazy, you can buy a prefab for a minimap here: http://www.gameprefabs.com/products/show/475
This is a helpful piece of code for positioning the player in the mini-map (C# this time!) http://www.joshrevilo.com/2011/11/minimap-in-unity3d-9-hours-in/
This is my favorite of the video tutorials, I was able to implement a basic version as described, and he’s providing solid support in the comment thread.
This tutorial shows how to make a non-rectangular non-texture shading mini-map in Unity3d.
This tutorial makes use of this shader http://www.unifycommunity.com/wiki/index.php?title=DepthMask
Another tutorial, this is a simplified version, and good to start with to grok the concepts involved
And here’s a few more: