This paper uses high-resolution images of nighttime luminosity to estimate a globally comparable measure of the size of metropolitan areas around the world for the years 2000 and 2010. We apply recently-proposed methodologies that correct the known problems of available nighttime luminosity data including blurring, instability of lit pixels overtime and the reduced comparability of night light images across satellites and across time. We then develop a protocol that isolates stable nighttime light pixels that constitute urban footprint, including low luminosity urban settlements such as slums, and excluding confounding phenomena such as highway illumination. When analyzed together with existing geo-referenced population datasets, our measure of urban footprint, can be used to compute city densities for the entire world. After characterizing some basic stylized facts regarding the distribution of urban sprawl, urban population and population density across world regions, we offer an application of our measure to the study of the size distribution of cities, including test of the Zipf's Law and Gibrat's Law.
While there is a broad consensus in the literature that there is a positive correlation between Internet usage and labor income in the richest countries, this link has not been proven in the developing world. This paper uses propensity score matching techniques and household survey data to estimate the effect of the Internet on wages in Colombia, a country that has experienced a relatively rapid diffusion of information and communications technology in recent years. The empirical results confirm that there is a positive and statistically significant relationship between Internet use and income in this country. Consistent with evidence gathered on developed countries in previous studies, the empirical results also suggest that workers in the middle of the skill distribution receive the lowest wage premium for using the Internet. However, contrary to most evidence from developed countries, low-skilled workers in Colombia enjoy the highest wage premium from Internet use, which illustrates the potential for new technologies to address inequality gaps between occupations.
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