When things are "scattered", it means that they are located randomly around a location. They're not straight, grouped together, or in order. Imagine a stack of cards which have been dropped on the floor:

The cards were scattered all over the floor.

"Scattered all ___" is completed by a variety of different words, depending on what location the things are scattered in:

There was trash scattered all along the side of the road.

Mr. Preston is planning on visiting several schools scattered throughout the state.

Soda bottles were scattered around the room.

My photo collection is scattered across three or four different computers.

As you can see, sometimes "all" comes after "scattered" but it doesn't always need to.