I may be the last to have figured this out, but in case I'm not: When you're trying to make a large world easily, it's no longer necessary to zero-edge your terrains in the terrain editor, because of one little checkbox in the replicator. Start by creating any terrain; you can "rescale terrain to fit working box" or not. Return to the assembly room. Insert a replicator object by choosing the second icon in the replicator menu and clicking in the window. Double-click the replicator to enter the editor. Choose auto-grid. Under replicated objects, click add and choose your terrain object. (You can also do this in the assembly room, in the "Instances" menu, by dragging the "terrain" instance onto "replicator", whereupon it will place itself under the replicator instance. Look at "assembly".)

Choose the number of duplicated terrains you want for the x and y axes. I also prefer to check "center grid." Leave the "Random transform of each object" settings at zero, but: CHECK THE SEAMLESS BOX. The settings look like the replicator screen above.

When you return to the assembly room, you'll see bounding boxes representing the new terrains that will show up when you render. I advise rendering before doing anything else: this isn't a perfect solution (notice the abrupt cliff artifact circled in yellow in the finished quick render). You can either adjust the original terrain's edges or go back to the replicator editor and have it create real instances; this will make the replicated terrains their own objects. And possibly give you enormous files, but also objects you can individually edit.

This isn't really earth-shattering, I suppose; but it surprised me that C5 could do it. OK, I'm easily surprised. But with just a couple of original terrain primitives and a couple of differing replicators, you can quickly build some large, fairly complex landscapes.

Hey, might not be earth shattering, but before you brought it up I never thought of replicating a terrain... so thanks for pointing it out. :) Christina

As a Carrara "neophyte" I find this information very useful! Thanks!