Recreating a map

Ok so idk if this is the correct category, in that case hope they move it to the right one.

So, i’m making a huge map with a mountain but there are so much useless terrain parts that make the map sooo slow and heavy and deleting them vould take like a month.

I was wondering, is there a plugin or some methods to have a grid of my map? i mean, a grid so i can create again the map basing on that and using his surface for recreating it without useless parts.

For example:


Once i got the surface i would like to copy it and paste it in a new place where i can recreate it without useless parts

Here is an example of map i would like to get the surface

If there is no plugin that could accomplish what i need i have an idea, make a huge grid of cubes/spheres and let them fall on the map, once they hit the surface they will stop and get anchored, here is an example

So basically:
I need a plugin to get the surface of a map so i can recreate it without useless terrain parts


A script that make a part anchor when collides with the terrain (just an explaination on how to do it is enough)