Placing Large Objects

Large items like the Arc de Triomphe, city walls, retaining walls, river water, and large rocks affect the placement of items around them.  It's very easy to click on them accidentally while doing something else, and the next thing you know you have a river hovering in the mountains.  Placing items back where they belong can be a difficult task if you don't have the coordinates, throwing off the placement of surrounding items and lots.

When placing large objects, take a moment to jot down the X, Y, and Z coordinates from the properties panel.  If your object is moved accidentally later, you can simply reenter the coordinates to replace the item.

Tracking the coordinates can also be helpful in editing items later.  For example, if you have lots of plants around the Ruined Walls, when you try to grab the plants later, you'll get the wall instead.  If you know the coordinates of the wall, you can simply move it out of the way while editing the surrounding landscape, and then restore it to its exact location when ready.

Ground fog can be a pain when it comes to editing the landscape under the effect (which I inevitably do, no matter how "done" I think I am when placing the fog).  If you have the fog pieces exactly where you want them, note the coordinates and delete the effects.  Add them back at the end using the coordinates.

Hope that helps!