Every time I terraform, the entire region changes. How can I stop this?

[AtomicShrink]

Any little change I make is making giant changes in my entire region, and now the whole place is destroyed. How do I fix this?

[Lindal Kidd]

Start by flattening things back out.

This YouTube tutorial may help.

I'll try to explain some things, too.

There are two ways to terraform (well, three, but we're not going to get into applying RAW terrain files): The Bulldozer and Land Selection.

The Bulldozer tool is that array of white vertical arrows you see when you have selected a land tool and move your cursor over the land. It varies in its size and the power of its effect with the Size and Strength sliders. The effect is applied when you hold your left mouse button and move your cursor over the land, like using a big paint brush.

If you have a big piece of land to work, and want to avoid cramps in your mouse finger, you can click the Select Land button (top item in the land tools palette). Then drag your mouse to select an area of land. SHIFT+Drag can be used to add to a selection. Your selection is bordered in yellow. If you have a selection made, and then select one of the other land tools such as Flatten, and click the Apply button, the effect will be applied to the entire selection at once. The Strength slider is also active in this mode.

This is the easiest way to flatten out a big area that you've messed up. Once you've done that, use the Bulldozer to "paint" in terrain features in finer detail.