@article{Usery_1992, title={Geographical Information Systems: Principles and Applications}, url={https://cartographicperspectives.org/index.php/journal/article/view/cp13-usery}, DOI={10.14714/CP13.1002}, number={13}, journal={Cartographic Perspectives}, author={Usery, E. Lynn}, year={1992}, month={Jun.}, pages={21–22} }