While working in the editor it is possible to hide assets that you aren't currently working on, which can make it easier to work on the map as you can hide areas/assets to allow you a clear view of the area you're working on. It can also improve performance within the editor as it's not drawing all the map assets while your working!

Anything you hide this way will still be visible ingame.  It is only hidden in the editor!

There are 2 ways of hiding assets.  Temporary hiding and grouping.


Temporary hiding:

There are 3 icons on the main toolbar.


The open eye icon means show only the assets selected. 
The closed eye hides any assets selected!
The eye with the 'X' unhides everything.

Basically what you do is highlight everything(including BSP) you don't need to work on then click the hide icon...or...click on the assets you are currently working on and click the open eye icon.  This will hide everything else in the editor windows. 

After hiding anything not needed you can easily work on the area that you need to without other areas obstructing your view.
Once you are done you can click the eye 'X' button and reveal everything again.


Grouping:

Grouping is like an extension to the temporary hiding functions.  With grouping you can select a collection of assets and group them then later on you can hide the various groups with a simple click rather than having to reselect everything again. 

I find groups very handy as you can keep related assets together.  For example I always have a sky group in my maps which say include the star sphere, nebula fogsheets, sun and planet assets etc...

To create a group select all the assets you want to group.  Next open the generic browser and select the 'Groups' tab.  Next click on the edit menu and select 'New'. Give this group a name and click OK. 

You'll now have a new group created which now contains all the assets you had selected.
Next to the group name there's a 'tickbox'.  While the box is ticked the group assets will be visible in the editor.  If the tickbox is unticked the assets will be invisible within the editor.

Later on you can also add aditional assets to any groups.  Select the assets you want to add.  Open the generic browser and go to the groups tab.  Next click on the edit menu and select the 'Add Selected Actors to Group' option.
Last but not least... Every mesh in the editor has a groups property which lists the groups that it is in.  You can manually add group names to this if the groups already exist!

Groups are very helpful when using the editor as it can keep it uncluttered while working on your map!