An important point to note is that, for cities in certain regions of the world, high cloud coverage during certain periods (during monsoon seasons, for example) constrains data availability, as indicated by the circular markers in panel A. These reflect cloudy months. Therefore, in the regression analysis of Section 3, city-month observations for which nighttime lights data are missing (i.e., for which it is not possible to calculate an SOL value) are dropped. Relatedly, all regressions also include a full set of country-specific month-of-year fixed effects to account for seasonal nighttime light trends at the country level, which may be related to cloud coverage, and also, potentially, atmospheric distortions.<sup>9</sup> Meanwhile, disease progression statistics (number of reported Covid-19 cases and deaths), and measures of both the stringency of NPIs (the stringency index) and economic support measures (the economic support index) were retrieved from _The Oxford Covid-19 Government Response Tracker (OxCGRT)_ (Hale et al., 2022). The stringency index measures the strictness of mobility limitation resulting from government-imposed measures, while the economic support index captures the strength of economic support policies (including cash assistance, tax cut, or debt relief) implemented to combat the negative economic impacts of the crisis. Both the NPI stringency and economic support indices track policy responses starting from January 2020. It is important to note that, while this data has time variation, it is mostly only available at the country level.<sup>10</sup> For select countries, Figure 3 shows the within-country variation in monthly Covid-19-related deaths, the stringency and economic support indices.

Returning to Figure 2, it can be seen that cities’ nighttime light trajectories also appear to be correlated with the trajectories of Covid-19 deaths in the corresponding countries. Broadly, periods of higher death rates at the national level are associated with sharp negative deviations of cities’ nighttime lights from their long-term trend growth paths. The sudden implementation of NPIs early in the pandemic is also associated with falls in economic activity in China and Italy but not in poorer economies like Bangladesh and Zimbabwe. This likely reflects differences in enforcement capacity across the countries. Panel B of Figure 2 shows that these patterns also broadly hold for Egypt and Saudi Arabia, but there is variation in the impact across cities within countries as well.

Using data from the GHS-UCDB, we also compiled variables related to various city characteristics, including the total land area, population, estimated GDP, and built-up area. For each city, an index of compactness — the Polsby-Popper Ratio (PPR) — was calculated based on its spatial extent to capture a city’s urban form. The length of roads within cities was derived from Open Street Map (OSM) data to capture a city’s infrastructure development. Summary statistics for all variables included in the analysis are given in Table A1 in the appendix.

> 9 In additional results reported in the appendix, we also show the robustness of our results to weighting observations based on the number of pixels within a city’s area that had more than one cloud-free day to address the related measurement error. In other words, these regressions give less weight to observations that are more contaminated by cloud coverage and which, therefore, are of lower quality.

10 During the earlier stages of the pandemic, most NPI and economic support measures were implemented at the national level, thereby making the absence of city-specific data less of an issue. For example, though the UK attempted locally targeted lockdowns between July and October of 2020, their efficacy varied by location and authorities reverted to nationwide lockdowns from November 2020 as cases rose. Similarly, France also reverted to a national state of emergency after a brief period of lifting the emergency between July and October 2020. This makes the measurement error implied by the use of the national NPI and economic support indices less of an issue during the first year of the pandemic. Subnational data is available for five countries (Brazil, Canada, China, United Kingdom and United States) at the state or equivalent level. We analyze this data as part of robustness checks reported in the appendix.

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