The concept of space is a little more abstract than the past few assignments.
The reason for this is because the idea is to make the empty space feel like the most important part of the photograph.
You will accomplish this by photographing objects that beautifully define the area that they contain. (I know this is confusing) but look.
In this example the buildings are what you see but the alleyway is what is important. The light helps to accentuate the alley.
Again here the light and the shape of the rocks make the cavern become the important part of the photograph.
Another way to emphasize space is to create an event that makes the air important
Sometimes just defining a side or only the bottom of the area is enough and then our eyes fill in the rest
The last way you may want to approach this assignment is to find fog, smoke or dust. This will make the air visible and in so doing will make the air take on an important part of you photo. As always light is critical in the success of this approach.