Other than on the map Forge World ? Seems like if i want to use any of the other maps from scratch, i would need to first go and delete all the items that have been placed. Is there a way to mass delete everything that's been placed on the default forge maps ? Thanks.
Press X on each of every item type and click delete all. You will have to do it for each type of item placed though I am afraid.
Unfortunately, the Forge is a very weak map editor you can't do basic tasks like selecting all same type items at once. It's very tedious to do most things in Forge. Bungie didn't make it easy to do most "housekeeping" chores. Halo is the most awesome game franchise on the Xbox, but Bungie doesn't know how to make a good map editor. It's a shame.
Forge is really a scenario editor rather than a map editor. It's the same thing as Sapien was in Halo:CE(PC). All your building blocks are basically scenery. Forge is a very powerful tool especially when you can switch to edit mode back to play mode on the fly. The physics are always active. I think the bad things are that we don't have full access to all tags in every map. Forge World is the only map where you can truly be creative. A full tag set would allow you to place any item in any map and not be limited at all. I think that is the major downfall of the system, not in the power of it.