This will show you how to work with GTKradiants regions.
regions is usefull if you make a map with a lots of brushes and
you are confused about the lines over the display... so you wanna
have for examble a single house to edit from the hole map.
so select the brushes you want to edit (eather select every single brush or make a big brush around all brushes you want to select and press "select inside". then press "region"
and "Set Selected Brushes"
then it should look like that:
to get the whole map shown again, easily press "Region" and "Off".
hope this is helping you.