We consider a two-parameter discrete generalized beta (DGB) distribution and propose its universal applications to study the size-distribution of the urban agglomerations across various countries in the world, where the urban agglomerations include the small and mid-sized cities along with the heavily populated cities. Our proposition is validated by an exhaustive study with the 3 decades' census data for India and China and census data of USA for a time window of 8 years. Moreover, we have studied the city size distributions for many different countries, like Brazil, Italy, Sweden, Australia, Uganda etc., from all the continents around the world according to the availability of the data. The detailed analyses exhibit a unique global pattern for the city size distributions, from low to high size, across the world with various geographic and economic conditions. Further analyses based on the entropy of the distribution provide insights on the underlying randomness and spreads of the city sizes within a country. The DGB distribution, a typical rank order (RO) distribution, through its two parameters, not only fits the data on wider range of city sizes better than the wellknown power law for all the countries considered, it also helps us to characterize, discriminate and study their evolution over time. * Electronic address: abhianik@gmail.com † Electronic address: sribbasu@gmail.com arXiv:1809.08786v3 [physics.soc-ph] 8 May 2019 that the domain is the natural numbers 1 to N instead of the interval (0, 1) of usual continuous beta distribution. Several RO distributions including the DGBD and its further generalizations have already been studied to provide good fits in the context of different count or rank-size data from arts and sciences [20][21][22][23][24][25][26]. In the present paper, our main contribution is to propose and illustrate that the DGBD can be successfully applied to provide a simple, yet excellent, universal fit to the city size data across different socio-economic countries. Our analyses show that the data for all countries under consideration follow, with a wonderful goodness-of-fit, the DGB distribution, a two parameter RO distribution, incorporating the product of two power laws defined over the complete data set -one measured from left to right and another in the opposite direction. For the vanishing value of one particular parameter, the DGB distribution simplifies to the usual Pareto law for the cities with heavy population (see Section II A). To understand the underlying process of the urban morphology, the Shannon entropy of the proposed DGB distribution has also been studied. Based on the two parameters of the distribution and the corresponding entropy, one can indeed discriminate and study the evolution of city distributions in different countries across the world.The rest of the paper is organized as follows. Sec. II deals with the mathematical formulation of the two-parameter DGBD. In the respective subsections A, B and C, we define our particular RO distribution and the corresponding S...