The streets system, encompassing avenues and boulevards, is fundamental to experiencing and understanding a city, defining blocks and distinguishing public, accessible spaces from private or semi-public areas. Streets serve as the public, democratic space where diverse citizens interact. Bill Hillier, founder of Space Syntax, argues that streets do not merely reflect societal divisions but can gather in space what society insists on dividing, considering their livability a key indicator of a strong civil society. In morphological and temporal terms, the streets system is the most stable element of urban form, offering greater resistance to urban transformation than plots or buildings, which have lesser durability over time.

Streets vary widely in shape, size, relationships with surroundings, and urban functions. A street's character is significantly influenced by other elements of urban form. These include the plots on either side; the buildings themselves, their height, and the ratio of height to street width; how buildings are sited on plots (e.g., near frontage for enclosure or set back for openness); and the entrances buildings offer. The distribution of space for pedestrians and vehicles—public or private, motorized or non-motorized—is also a crucial analytical aspect, as noted in works like Allan Jacobs' "Great Streets."

Diverse examples illustrate this variety. New York City features Broadway, unique for its irregular pattern within Manhattan's orthogonal grid, and the prominent 5th Avenue (10 km long, 30 m wide). Paris's Avenue des Champs Elysées, a symbol of Baron Haussmann's 19th-century intervention, is a grand axis (2 km long, 70 m wide in its western part) with homogeneous buildings, where building height is clearly inferior to street width, creating a strong sense of openness. It boasts a strong presence of trees and varied functions like shops, cafes, and cinemas, forming part of a longer axis linking La Defense and the Louvre. Siena's Via Rinaldini, a small medieval street less than 50m long and 5m wide, is directly linked to the city's famous square, notable for buildings whose height is clearly higher than the street width. Amsterdam's Reguliersgracht, part of the 'ring of canals' from the 17th century, has a unique cross-section (30 m wide, 600 m long) that includes a canal and, on each side, a street with distinct spaces for pedestrians, vehicular traffic, and car parking.

The public spaces system of a city extends beyond streets for movement to include open spaces for permanence, such as squares and gardens, which also exhibit significant diversity in form and function. New York's Times Square, located at the intersection of Broadway and 7th Avenue, is morphologically an intersection yet is consistently bustling with people, serving as the heart of the Theater District with numerous cultural and commercial activities, accentuated by attractive neon lights, and famed for its New Year’s Eve celebration. Paris's Place Georges Pompidou (175 m long, 70 m wide) has a clearly defined rectangular shape and a distinctive sloping surface that invites diverse activities and establishes a strong artistic dimension due to the Centre Georges Pompidou. The nearby Place Igor Stravinsky complements it with modern sculptures. Siena's Piazza del Campo, a 12th-century Italian square, is famous for its shell shape and wide sloping surface, delimited by notable palazzi of varying heights, with its lowest point at the town hall; it hosts events like the Palio horse race. Meidan Emam in Isfahan, Iran, is a grand rectangular square (520 m long, 160 m wide), bordered by a continuous two-story building volume with a double colonnade. It includes UNESCO-classified mosques and a palace, provides access to the Bazaar, and is intensively used by local people for many activities, distinct from the other examples due to a lesser presence of foreign tourists.

The diversity seen in streets is mirrored in squares, even within the same city. Paris's Place Vendome, an early 18th-century square in the Tuileries area, is rectangular with octagonal corners (140 m long, 120 m wide). It is crossed by only one street and is composed of architecturally homogeneous buildings housing fashionable shops, illustrating how urban fabrics vary significantly within a single metropolis.