## 6 Conclusions  
During the process of urbanization, it is important to measure the human occupation of nature and maintain the sustainable development of society. Using EF-NPP, this article theoretically improved  
Figure 7: The comparison of average equivalence factors and yield factors with [PERSON]’s study.  
the shortcomings of the ecological footprint model in spatial analysis, quantitatively measured the temporal change of the ecological footprint and spatially located the ecologically fragile areas. The results of this article prove that the ecological footprint can be used to indicate the pressure humans put on nature, by comparing it with the ecological capacity. Based on the results we found, policy suggestions for the sustainable development and ecological civilization of Xuzhou city were proposed. The main conclusions of this article are as follows:  
(1) The natural capital that humans require in Xuzhou central area increased, such that the bio-productive land could not support the demand of human living and production activities, and the ecological situation became extremely unsafe.  
(2) The spatial pattern showed the ecologically fragile areas and the unbalanced ecological situation in Xuzhou central area. The ecological pressure was higher in the northeast and southwest of Xuzhou central area.  
(3) Policy measures should be adopted to promote the harmonious development of ecology and the economy. The government should control the increase of the ecological footprint and improve the ecological capacity in the center of Xuzhou to alleviate conflicts between humans and the land. The urban space in different areas should be optimized to achieve the comprehensive and coordinated development of Xuzhou central area. The government should pay attention to increasing the investment in ecological civilization construction, improving the ecological environmental protection system as soon as possible in order to coordinate the development of the social economy and ecological environment, and take the road of sustainable development. The EF-NPP could be applied in regional ecological environment monitoring, and has profound implications for ecological security and city development planning.  
(4) The EF-NPP model measures the equivalence factors and yield factors by NPP instead of the production and consumption, which avoids deviation in the calculation. Combining the calculation values with land use data can spatialize the ecological footprint, ecological capacity and ecological deficit, thus making up for the shortcomings in the spatial analysis of ecological footprint analysis.  
(5) In future studies, the accuracy of land use data needs to be improved. For example, the MODIS data could be replaced by Landsat data with a higher resolution. Furthermore, the ecological footprint model can continue to be improved to be more comprehensive.  
Conceptualization, Y.L.; Data Curation, Y.L.; Formal Analysis, Y.L.; Funding Acquisition, X.L.; Methodology, Y.L.; Project Administration, X.L.; Software, H.N.; Supervision, X.L. and C.X.; Visualization, H.N.; Writing-Original Draft, Y.L. and H.N.; Writing-Review & Editing, X.L., X.C., C.X., D.J. and H.F.  
This study was supported by National Natural Sciences Foundation of China (Grant No. 71473249, Grant No. 71704177 and Grant No. 71874192), Fundamental Research Funds for the Central Universities (2017 WB05), Key Projects of Jiangsu Provincial Social Science Fund (15 EYA002), Open Fund for the Key Laboratory for Coastal Zone Development and Protection of the Ministry of Land and Resources (2017 CZEPK10) and National College Students Innovation Training Program (201810290034).  
The supports of China University of Mining and Technology and School of Environment Science and Spatial Informatics are acknowledged.  
The authors declare no conflict of interest.