ABSTRACT
This chapter focuses on selecting map projections for representing continuously occurring and abruptly changing phenomena. The predominant visual analysis tasks for continuous and abruptly changing phenomena are to identify values at specific single locations of interest, compare values across multiple locations. The chapter provides examples to demonstrate the impact of projection on choropleth mapping. It discusses the numerous projection-related challenges with respect to specific projection characteristics. Interpretation of choropleth maps is largely based on comparison of values for large areas on the map or across multiple regions. Conformal projections preserve local angles at the expense of relative area, so for global-scale choropleth maps this means that it will be difficult to make accurate comparisons of area covered by any given attribute. For small-scale choropleth maps, the one best alternative to an equal area projection is a “compromise” projection. These projections preserve no specific property, but often are designed for a balance between distortion and aesthetics.
