Figure 1. Location of Yuen Long town, Hong Kong(drawn by the author)

Figure 2. Theoretical framework of nutrient flow in the field of urban metabolism(developed by the author)

Figure 3. Land use occupation ratio of the three parts(drawn by the author)

Figure 4. Value of the three parts in four dimensions at meso scale(drawn by the author)

Figure 5. Holistic nutrient(N: t yr^-1) flow in Yuen Long town system(drawn by the author)

Figure 6. Mapping of spatial N flow example in Yuen Long town at macro scale(drawn by the author)

Table 1. Review of the scales and aspects in the field of nutrient balance research