Jane Jacobs’ rules for cities are timeless.

Urbanists across the globe are celebrating the life and legacy of Jane Jacobs —the 100^th anniversary of her birth.

Jacobs is arguably the most influential figure in the history of urban planning and placemaking—an interesting distinction because she was not formally educated in the discipline.

But what she lacked in academic credentials she more than made up for as a writer and observer and her seminal book—“The Death and Life of Great American Cities” has served as a bible for mayors, planners, architects, designers and anyone who loves cities since it was published in 1961.

Jane Jacobs said that for cities to thrive they need four conditions:

The first is that city districts must serve more than two functions so that they attract people with different purposes at different times of the day and night.

Second, she believed city blocks must be small with dense intersections that give pedestrians many opportunities to interact.

The third condition is that buildings must be diverse in terms of age and form to support a mix of low-rent and high-rent tenants.

Finally, a district must have a sufficient density of people and buildings.

The four concepts are really quite simple, yet so many cities seem to get it wrong. Sadly, density has become a loaded word and many cities have torn down their older and more interesting buildings.

Perhaps, if we changed dense to vibrant, maybe perceptions would change. Or maybe we are forever doomed to a battle between those who value design and sustainability against those who worry about traffic and a shortage of parking.

Still, most can agree that there has been a lack of an evidence-based approach to city planning for decades and it has ruined cities all over the world. What results are codes that in some cities prevent a mix of uses or if they do permit them, innovation is stifled by arbitrary numbers. Are 30 units to the acre—too much or too little for a sustainable downtown? Will 38 foot height limits preserve charm or prevent quality retail or design from occurring due to low ceilings?

Regardless of the politics of land use– and they are fraught– fact based planning is on the way if we choose to indulge.

Data-mining techniques are finally revealing the rules that make cities successful, vibrant places to live. And researchers are putting Jacobs’ work to the test.

Thanks to the work of Marco De Nadai at the University of Trento and a few colleagues, urban data is being gathered to test Jacobs’s conditions and how they relate to the vitality of city life. The new approach heralds a new age of city planning in which planners have an objective way of assessing city life and working out how it can be improved.

De Nadai and colleagues gathered this data for six cities in Italy—Rome, Naples, Florence, Bologna, Milan, and Palermo.

Their analysis is straightforward. The team used mobile-phone activity as a measure of urban vitality and land-use records, census data, and Foursquare activity as a measure of urban diversity. Their goal was to see how vitality and diversity are correlated in the cities they studied.

The results make for interesting reading.

De Nadai concludes that land use is correlated with vitality. In cities such as Rome, mixed land use is common. However, Milan is divided into areas by function—industrial, residential, commercial, and so on.

“Consequently, in Milan, vitality is experienced only in the mixed districts,” he said.

The structure of city districts is important, too. European cities tend not to have the super-sized city blocks found in American cities. But the density of intersections varies greatly, and this turns out to be important. “Vibrant urban areas are those with dense streets, which, in fact, slow down cars and make it easier for pedestrians to cross,” the researchers said.

Jacobs also highlighted the importance of having a mixture of old and new buildings to promote vitality. However, De Nadai and company say this is less of an issue in Italian cities, where ancient buildings are common and have been actively preserved for centuries. Consequently, the goal of producing mixed areas is harder to achieve. “In the Italian context, mixing buildings of different eras is not as important as (or, rather, as possible as) it is in the American context,” he said.

Nevertheless, the team found that a crucial factor for vibrancy is the presence of “third places,” locations that are not homes (first places) or places of employment (second places). Third places are bars, restaurants, places of worship, shopping areas, parks, and so on—places where people go to gather and socialize.

The density of people also turns out to be important, too, just as Jacobs predicted. “Our results suggest that Jacobs’s four conditions for maintaining a vital urban life hold for Italian cities,” concludes De Nadai.

They go on to summarize by saying: “Active Italian districts have dense concentrations of office workers, third places at walking distance, small streets, and historical buildings.”

That’s an interesting study that has the potential to have major impact on city planning. The lack of an evidence-based approach to city planning has resulted in numerous urban disasters, not least of which was the decline of city centers in the U.S. in the 1950s, 1960s, and later.

This new era of city science could change that and help create vibrant, vital living spaces for millions of people around the world.

In that regard, Jane Jacobs’ influence will live on.