The heart of Allan Jacobs’ classic book on street-level urban form and design, Great Streets, features dozens of hand-drawn figure-ground diagrams in the style of Nolli maps. Each depicts one square mile of a city’s street network. Drawing these cities at the same scale provides a revealing spatial objectivity in visually comparing their street networks and urban forms.
We can recreate these visualizations automatically with Python and the OSMnx package, which I developed as part of my dissertation. With OSMnx we can download a street network from OpenStreetMap for anywhere in the world in just one line of code. Here are the square-mile diagrams of Portland, San Francisco, Irvine, and Rome created and plotted automatically by OSMnx:
The top row depicts the late 19th century orthogonal grids of Portland, Oregon and San Francisco, California. Portland’s famously compact walkable blocks are clearly visible but its grid is interrupted by the Interstate 405 which tore through the central city in the 1960s. In the bottom row, the business park in suburban Irvine, California demonstrates the coarse-grained, modernist, auto-centric urban form that characterized American urbanization in the latter half of the 20th century. In stark contrast, Rome has a fine-grained, complex, organic form evolved over millennia of self-organization and urban planning.
Remember these are all at the same scale: one square mile. Compare the block sizes and intersection density in Portland to those in Irvine. Compare the orthogonal grid in San Francisco and the modernist simplifications of Irvine to the complex mesh of pedestrian paths, passageways, and alleys comprising much of the circulation network in Rome.
Above, we see New York, Paris, Tunis, and Atlanta. Manhattan’s rectangular grid originates from the New York Commissioners’ Plan of 1811. You can see Broadway weaving diagonally across it. At the center of the Paris square mile lies the Arc de Triomphe, from which Baron Haussmann’s streets radiate outward, remnants of his massive demolition and renovation of 19th century Paris. At the center of the Tunis square mile lies its Medina, with a complex urban fabric that evolved over the middle ages. Finally, Atlanta is typical of many American downtowns: fairly coarse-grained, disconnected, and surrounded by freeways.
One final example: square miles of central Boston, Jumeirah circle in Dubai, suburban northeastern Sacramento, and Osaka, Japan. What can you tell about these cities from their street patterns?
Several more examples and all the code to reproduce these diagrams are in this notebook in OSMnx’s GitHub repo. You can adapt it to visualize any street network anywhere in the world. For more info, check out the paper about OSMnx.