Chen, Wei, Krista Wheeler, Yungui Huang, Simon Lin, Daniel Sui, and Huiyun Xiang. “Evaluation of Spatial Accessibility to Ohio Trauma Centers Using a GIS-Based Gravity Model”. Journal of Advances in Medicine and Medical Research 10, no. 7 (August 24, 2015): 1-10. Accessed December 4, 2021. https://journaljammr.com/index.php/JAMMR/article/view/13508.