I try to make my own map, but when I try to click on this 'block' with the selecter tool, but i cant find it. This 'block' is BTW all around my map
Imagine the area to build in as a big invisible box. At the very bottom, you will just hit an invisible barrier that you can drive on, and it will smash your car too. There is no way to remove this, but I suggest you build your map above this, otherwise you will never drive on the terrain, you will drive on this invisible plane. Hope this helped.
we don't very well on your picture. maybe it come from of one of your own static objets. sometime the collisions aren't at the good place in the editor , you have a function for show the collision