That's an interesting observation about urban furniture! You're right to notice a mix. In many cities, you'll find both round/cylindrical trash cans and rectangular ones, each serving different purposes.
Round or cylindrical bins are very common in parks, plazas, and along pedestrian walkways. Their 360-degree design makes them accessible from any angle, which is ideal for high-foot-traffic areas. They often have a classic, unobtrusive look and are usually mounted on a single pole. The cylindrical shape is also structurally strong and resists tipping in windy conditions.
On the other hand, rectangular trash cans are frequently seen on busy streets, near commercial buildings, or integrated with other street furniture like bus shelters and benches. Their flat backs allow them to be placed flush against walls or poles, saving sidewalk space. They often have a larger capacity and can be part of a modular system that includes recycling compartments.
So, it's not one or the other. The choice often depends on the location's needs: aesthetics, space, expected waste volume, and ease of collection by sanitation crews. You'll likely see cylindrical bins in more open, scenic areas and rectangular ones in dense, space-constrained urban corridors. The diversity in design helps cities manage waste more effectively while contributing to the streetscape's character.