Having issues with tiling/stretching

Hello! Recently I have been trying to create environments, but I keep running into the following issue. After setting up the material(s) and setting up the lighting, the map looks like this:

As you can see, it’s horribly tiled. I have been searching for a way to prevent this tiling from occurring, and the only thing I found was to change the material’s mapping scale. However, this only causes the material to become enormously huge on the landscape.

So can I fix this tiling issue without stretching the material to ridiculous size?