But after Haussmann, the high-BC nodes form a more open, widely spaced system of key channels, somewhat like the vein network of a leaf. In other words, Haussmann’s avenues and boulevards helped to prevent routes becoming funnelled through the congested city centre, and gave Paris space to breathe.
The new roads also altered the typical shape of blocks. It’s been found previously that many urban road networks tend to intersect at right angles, dividing up the space ever more finely into square or rectangular blocks a bit like the crack networks of ceramic glazes. That’s what Paris looked like before the 1850s. But the new boulevards sliced boldly through this grid, creating a wider variety of block shapes, especially triangles and elongated rectangles.
So whether the Second Empire reforms transformed the face of Paris is a subtle question. Some of the changes over the 19th Century, such as higher street density and increase in intersections, might have happened anyway thanks to the growth in population. In other ways, Haussmann stamped a “non-natural” geometry on the city’s evolving network. Although Haussmann’s plans were criticised both at the time and by architects later, it looks as though they did a pretty good job, making the city centre less congested in a way that Parisians still benefit from today. London, in contrast, missed its chance: the grand new streets proposed by Christopher Wren after the Great Fire in 1666 weren’t built in time to prevent the city’s natural, spontaneous evolution from reasserting itself.
All the same, using the tools that Barthelemy and colleagues have developed, it might now be possible to probe Haussmann’s scheme more closely. One question, for example, is how close it came to finding the very best solution to the problems it tackled.