Roth, Robert E., Cynthia A. Brewer, and Michael S. Stryker. “A Typology of Operators for Maintaining Legible Map Designs at Multiple Scales”. Cartographic Perspectives0, no. 68 (March 1, 2011): 29-64. Accessed June 15, 2021. https://cartographicperspectives.org/index.php/journal/article/view/cp68-roth-et-al.