Three key vital signs make up the “urban pulse” of a city

三大关键生命体征构成了城市的“城市脉搏”

People often speak metaphorically of the heartbeat or pulse of a city, but according to the authors of a new paper published in the Proceedings of the National Academy of Sciences, cities do indeed have an “urban pulse”—an indication of urban “metabolic activity” that can be measured to suss out telltale patterns. And those patterns could help inform future public policy around urban planning. 人们常以“心跳”或“脉搏”来隐喻城市，但根据发表在《美国国家科学院院刊》（PNAS）上的一篇新论文，城市确实存在一种“城市脉搏”——这是一种可以被测量并用于探究潜在模式的城市“代谢活动”指标。这些模式有助于为未来的城市规划公共政策提供参考。

The precise definition of urbanization has shifted over the centuries. Zhe Zhu of the University of Connecticut and his fellow authors adopted a broad version for their study. It features fundamental “processes of concurrent change in at least six dimensions, including demography, economy, infrastructure, environment, governance and culture,” they wrote. “Together they give rise to outcomes, measurable results of the process, such as population growth, urban land expansion, GDP growth, and innovation.” 几个世纪以来，城市化的精确定义一直在演变。康涅狄格大学的朱哲（Zhe Zhu）及其合著者在研究中采用了广义的定义。他们写道，城市化包含“在人口、经济、基础设施、环境、治理和文化等至少六个维度上同时发生的基本变化过程。这些过程共同产生了可衡量的结果，如人口增长、城市土地扩张、GDP增长和创新。”

Their chosen metrics reflect this dynamic view: Cities are not static grids but “living, adaptive ecosystems.” “For decades, we had just been capturing the outcome of urbanization—a house that’s been built, or a road expansion,” said Zhu. “But you don’t really see the dynamics within an urban area. This is going to be a very impactful tool influencing not only top-down policy decisions from governments but also bottom-up decisions from everyday people navigating their cities.” 他们选择的指标反映了这种动态视角：城市不是静态的网格，而是“充满活力的适应性生态系统”。朱哲表示：“几十年来，我们只是在捕捉城市化的结果——比如建好了一栋房子或扩建了一条道路。但你并没有真正看到城市内部的动态。这将是一个非常有影响力的工具，不仅能影响政府自上而下的政策决策，也能影响普通民众在城市中生活时自下而上的决策。”

One day we may be able to check a neighborhood’s “urban pulse” while house-hunting, for instance, or while scouting potential locations for a new business. Thanks to advances in remote sensing and various analytical methods, it’s possible to gather multidimensional data from a variety of sources, such as satellite imagery, or geolocated mobile or social media data. Zhu et al. got their data from the NASA Harmonized Landsat and Sentinel-2 databases to analyze new construction, repairs, improvements to infrastructure, green space expansions, and demolitions in six different cities: Seattle, Shenzhen, Lagos, Mumbai, Dubai, and Mexico City. 未来，我们或许可以在买房或为新业务选址时，查看某个社区的“城市脉搏”。得益于遥感技术和各种分析方法的进步，我们现在可以从卫星图像、地理定位移动数据或社交媒体数据等多种来源收集多维数据。朱哲团队利用美国国家航空航天局（NASA）的“协调陆地卫星与哨兵-2号”（Harmonized Landsat and Sentinel-2）数据库，分析了西雅图、深圳、拉各斯、孟买、迪拜和墨西哥城这六个城市的新建项目、维修、基础设施改善、绿地扩张和拆迁情况。

Three key vital signs

三大关键生命体征

Their analysis revealed three distinctive “vital signs” for monitoring cities. First, urbanization is “spiky”: There are sharp, short-lived spikes in activity, not smooth continuous growth. The best example of this, per the authors, is Dubai, whose coastal areas showed very large spikes in redevelopment activity—most notably capital-intensive projects like luxury towers or mixed-used buildings. Shenzhen’s spikes, by contrast, were more clustered, “reflecting the city’s capacity for rapid, state-led mobilization of capital and construction,” they wrote. 他们的分析揭示了监测城市的三个独特的“生命体征”。首先，城市化是“尖峰式”的：活动呈现出剧烈且短暂的峰值，而非平滑的持续增长。作者认为，最好的例子是迪拜，其沿海地区的再开发活动出现了巨大的峰值，尤其是豪华塔楼或混合用途建筑等资本密集型项目。相比之下，深圳的峰值更为集中，他们写道，这“反映了该市在国家主导下快速动员资本和进行建设的能力”。

Second, urbanization is cyclical and non periodic: There are distinct phases of building/expansion, a peak and stabilization, followed by relative decline or dormancy. And no two cities are exactly alike. The patterns for specific cities aren’t predictable like temporal seasons, reflecting instead unique elements of each. Lagos, for instance, has fragmented and uneven cycles, with some neighborhoods showing lulls lasting many years punctuated by occasional periods of heightened activity. Dubai has highly irregular, more frequent cycles of expansion and contraction. 其次，城市化是周期性且非定期的：建设/扩张有明显的阶段，包括高峰和稳定期，随后是相对衰退或沉寂期。没有两个城市是完全相同的。特定城市的模式不像季节那样具有可预测性，而是反映了每个城市独特的要素。例如，拉各斯的周期零散且不均匀，一些社区会出现长达数年的沉寂，其间穿插着偶尔的活动高峰。迪拜则表现出高度不规则、更频繁的扩张与收缩周期。

Finally, urbanization is asynchronous: Even within cities there is substantial variance among neighborhoods. The process does not occur at coordinated rates or times, with each neighborhood exhibiting its own rhythm. Just because there is a major spike in activity in Dubai’s Al Mamzar region, that doesn’t mean the same thing is happening in Al Jaddaf or Mirdif. 最后，城市化是异步的：即使在同一个城市内部，不同社区之间也存在巨大差异。这一过程并非以协调的速度或时间发生，每个社区都有自己的节奏。迪拜Al Mamzar地区的活动出现大幅增长，并不意味着Al Jaddaf或Mirdif地区也在发生同样的情况。

One notable exception is the synchronized dip in activity during the COVID-19 pandemic, which caused shutdowns all around the world—a phenomenon the authors likened to cardiac arrest. Even then, there were significant differences in patterns among cities (and intra-city neighborhoods) in terms of how cities recovered from the shutdowns. “It’s like in human beings,” said Zhu. “When you get a disease, it’s not going to show up exactly the same in different people.” 一个值得注意的例外是新冠疫情期间全球活动同步下降，导致世界各地停摆——作者将这种现象比作“心脏骤停”。即便如此，不同城市（以及城市内部社区）在疫情后的恢复模式上仍存在显著差异。朱哲说：“这就像人类一样，当你生病时，不同人的症状表现是不完全相同的。”

“Collectively, these results suggest that urbanization is a mosaic process, produced through overlapping but uncoordinated pulses of activity that vary across space and time,” the authors concluded. And while heart-related arrhythmia is bad for one’s health, they think that this “urban arrhythmia” is a sign of resilience in cities. “By decoupling development cycles, cities avoid the overheating, labor shortages, and infrastructure collapse associated with total synchronization,” they wrote. “The lack of coordination may not be a failure of planning, but an adaptive mechanism that distributes urban stress over time.” 作者总结道：“总的来说，这些结果表明城市化是一个马赛克式的过程，由在空间和时间上各不相同、重叠但互不协调的活动脉冲产生。”虽然心脏心律失常对健康有害，但他们认为这种“城市心律失常”反而是城市韧性的标志。他们写道：“通过解耦发展周期，城市避免了因完全同步而导致的过热、劳动力短缺和基础设施崩溃。这种缺乏协调的现象可能并非规划的失败，而是一种随时间推移分散城市压力的适应性机制。”