In my experience, urban outdoor furniture is not usually limited to complete sets. Most of the time, it depends on what you are buying and where you are buying it. For public spaces and commercial projects—think benches, litter bins, bollards, planters, cycle racks, and single seats—the furniture is very often sold per piece. That makes sense because designers and facility managers usually need to fit a specific layout, replace one damaged item, or mix different products from the same range. Many suppliers also offer modular systems, so you can buy individual modules and arrange them to suit a plaza, campus, or streetside setting.
Complete sets are more common in retail and hospitality contexts. If you are looking at outdoor dining tables and chairs, lounge groups, or matching patio conversation sets, those are frequently sold as a package. It is convenient for buyers who want a coordinated look without matching every item separately. Some commercial suppliers also sell set packages for projects, but that is usually a configuration choice rather than the only option.
So the short answer is: urban outdoor furniture is typically available per piece, and complete sets are also common in certain product categories. If you are specifying for a project, I would always check the product listing carefully. Look for whether the price is for one item, a pair, or a full set, and confirm what is included—cushions, fixings, anchors, and delivery. For replacement and maintenance, buying per piece is usually more practical; for a quick coordinated installation, a complete set can be the easier route.