Blending World Map Projections

The idea of designing a new map projection via combination of two projections is well established. Some of the most popular world map projections in use today were devised in this manner. One construction method is to combine two source projections along a common parallel (for example, Goode’s homolosine combines the sinusoidal and the Mollweide projections). A second method calculates the arithmetic means of two projections (for example, the Winkel Tripel projection). These two methods for creating new world map projections are included in the latest version of Flex Projector. Flex Projector, a freeware mapping application, offers a graphical approach for customizing existing projections and creating new projections. The Mixer is a new feature in the latest version that allows the user to blend two existing projections to create a new hybrid projection. Additional to the two established combination methods, the software includes a new method for blending projections specific to its visual design approach. With this new method, a unique trait of one projection is transferable to a second projection. For example, the straight parallels of the Eckert IV projection are replaceable with the arced parallels of the Winkel Tripel projection. Flex Projector allows for the blending of four different projection traits separately or in combination: (1) the horizontal length of parallels, (2) the vertical distance of parallels from the equator, (3) the distribution of meridians, and (4) the bending of parallels. With this new approach to projection blending, creating new projections becomes simple and easy to control. The integration of the three methods into Flex Projector allows the user to transform raster and vector data to new projections, and to evaluate distortion characteristics of new projections. As an applied example, the paper introduces the new Pacific projection that is a blend of the Ginzburg VIII and Mollweide projections.