Having gone to art school, one of the first things that you are taught is that negative space is the space around and between the subject(s) of an image. A landscape should, in most cases, make use of both the positive and negative space as well. Silhouettes are reliant on backgrounds -- garden beds are reliant on the bed floor. Manipulating the negative gives shape to your subject whether it be in a painting, photograph, or landscape design. Yes, negative spaces in landscapes can be at the scale of a body of water, large fields of grass or paved walkways, but when addressing smaller urban landscapes the same rule applies.
There is a building down the street from Sprout Home Chicago that each time I walk by the patterned glass block façade I imagine how I could use it in a landscape design (right before I walk in to the light post). The contrast of negative and positive space creates a pattern that is mesmerizing and calming, a place to rest my eye on a busy street. They could easily be treated like pavers in a small garden setting. There is actually a growing trend in the permeable paver market that focuses on being able to purposely plant in the negative space of the pavers therefore creating a living pattern that is both attractive and practical.
When deciding what material to utilize in the creation of your garden's negative space don't be afraid to think outside the box (pun intended), like creating a pattern with repurposed material such as the above mentioned glass block -- not every negative space has to be grass. If you do implement a pattern for the negative space, keep it simple. Limit your color palette and texture to reinforce the design. Remember: you need the negative to draw focus and form the positive.