StreamStats has limited functionality in some areas. These areas are indicated on the map with a cross-hatch pattern: . StreamStats either can't delineate the drainage area in these areas, or there is some other limitation, such as not being able to solve regression equations there. If you try to do a delineation in those areas, you will see a message explaining what the situation is in that case. Some of the areas allow some functionality, but others don't allow you to do delineations at all. It just depends on the circumstances. The way to find out is just to attempt a delineation there.