Rapid and large-scale urbanisation is one of the defining phenomena of the past few decades. Still, several critical 'puzzles' about city development remain poorly understood. Although the dramatic increase in the size of many cities has been experienced, the commute distance and time seem to have remained remarkably stable. In Potato Project, we analyse 50 million individuals' location data from over 234 cities in China and empirically prove the scale invariance of commuting distance. To visualise this phenomenon, we reveal the fractal nature of cities. We adopt Frei Otto's Woolly Path concept to connect a set of nodes, in this case, using commuting patterns from home and work locations, to create a minimal path network. All cities present a universal 'inverted U-shape' of the average commuting distance and time as a function of the distance from the city centre, indicating that the city centre's attraction to citizens is bounded. Furthermore, it shows how human mobility behaviour determines the emergence of macroscopic urban spatial structure and sheds light on the complex interplay between micro-level human decisions and macro-level urban phenomena. ​