where, Gjt are the standardized per capita GDP for area j in year
t (using the same structure of Eq. (2-3)). The
√
2
2 (Ijt − Gjt) is the
straight-line distance from point (Ijt, Gjt) to the diagonal (y = x)
(Fig. 3). If a region falls in the space where I > G, it means that the
region has a relative good balance between environmental protection
and economic development, which could lead to a long-term
sustainable development. In contrast, if a region falls in the space
where I < G, it means the region overused its environmental capacity
for its economic growth, which is unsustainable in the long term.
Overall, the higher R indicates a more sustainable development.