REFERENCES
- Heffron, S. G., and R. M. Downs, eds. 2012. Geography for Life: National Geography Standards, 2nd ed. Washington, DC: National Council for Geographic Education.
- Sinton, D. S., S. Bednarz, P. Gersmehl, R. Kolvoord, and D. Uttal. 2013. The People's Guide to Spatial Thinking. Washington, DC: National Council for Geographic Education.