Low poly map from blender : collider

Hello,
i have question. Using this tutorial :

i made my map ( without trees ). Then I export in to uinity 3d. I Add default player (fps) and when i add to my map "Terrain Collider" my player drop down under the map. I must add "Mesh Collider" and it is OK ( i can run on map ). My question is : Why Terrarin Colider don't work ? Is is good idea to make map in Blender? ( i don't know how make low poly terrarin in unity ).

Thank You for help : )

 

I found something like this:
http://wiki.unity3d.com/index.php?title=Object2Terrain

but if i use it i lost edges

 

Because that only works with a Terrain. You don't have a Terrain there, you have a Mesh. MeshCollider works with Meshes, TerrainCollider works with Terrains.

If you want a low-poly terrain, then yes, Blender is a fine way to make it.

 

Thank You very much for help : )