I welcome this new approach with great interest. In fact, its simplicity is its strength. Population and density are concepts that can be understood and used worldwide. As you make clear, this increases transparency and allows for a much more effective international monitoring process. However, what we gain on one side, we lose on the other. We get simple global tracking of geographic features (population settlements) and global goals (such as the SDGs), which in turn is a big step forward. But we are losing political relevance. The concepts of rural, urban or suburban areas are used by decision-makers to adapt social, economic or environmental measures. And population density is rarely the right driver for this.
If the definitions are so different from one country to another, it is because they have different political visions of space that matter in certain contexts. And when international comparisons reduce this diversity, they unfortunately become less useful at the national/territorial level. Functionality is the compass that guides territorial policy today, and settlement-based geographic boundaries are simply no longer sufficient to guide policy-making. Urban society is generally stratified. Spatially, cities are formally or informally separated along ethnic, economic, and racial lines. People who live, work and play relatively close to each other, in separate areas, and connect with different people, forming ethnic or lifestyle enclaves or, in areas of concentrated poverty, ghettos. While in the United States and elsewhere, poverty was associated with the city center, in France it was associated with the suburbs, areas of urban development that surround the city proper. In Europe and North America, the racially white majority is empirically the most segregated group. Western suburbs and, increasingly, gated communities and other forms of « privacy » around the world allow local elites to separate into safe and exclusive neighborhoods.
 In a radial structure, the main roads converge at a central point. This form could evolve from successive growth over a long period of time, with concentric traces of walls and citadels marking the former city limits. In recent history, these forms have been supplemented by ring roads that moved traffic to the outskirts of a city. Dutch cities such as Amsterdam and Haarlem are structured as a central square, surrounded by concentric canals that mark each extension. In cities like Moscow, this trend is still clearly visible. Factories and slums emerged as regular features of the urban landscape.  Writers, painters and filmmakers have created countless works of art for the urban experience. Classical and medieval literature encompasses a genre of descriptions that deal with the characteristics and history of the city. Modern authors such as Charles Dickens and James Joyce are famous for their impressive descriptions of their hometowns.
 Fritz Lang got the idea for his influential 1927 film Metropolis when he visited Times Square and marveled at the neon lights at night.  Other early cinematic depictions of cities in the twentieth century generally portrayed them as technologically efficient spaces with well-functioning automobile traffic systems. However, in the 1960s, traffic jams began to appear in films such as The Fast Lady (1962) and Playtime (1967).  Urban structure generally follows one or more basic patterns: geomorphic, radial, concentric, rectilinear, and curvilinear. The physical environment usually limits the form in which a city is built. If you are on the mountainside, the urban structure can rely on terraces and winding roads. It can be adapted to their livelihoods (e.g. agriculture or fishing). And it can be configured for optimal defense considering the surrounding landscape.  Beyond these « geomorphic » characteristics, cities can develop internal models due to natural growth or urban planning.
The degree of urbanisation method classifies cities, municipalities and high-density areas, as well as rural areas in a simple and transparent way. By standardizing the classification approach and applying it globally, it can help identify and measure the effectiveness of policies in different countries that improve the quality of life in these areas. It will also help monitor access to services and infrastructure and other SDG indicators in a way that allows meaningful comparisons and aggregations. This method is tested and implemented in many countries around the world.