Map Projections and Distortion Visualization

Floating Ring: A New Tool for Visualizing Distortion in Map Projections


We present a new method for interactive visualization of distortion in map projections. The central idea is a floating ring on the globe that can be interactively positioned and scaled. As the ring is manipulated on the globe, the corresponding projection of the ring is distorted using the same map projection parameters. We apply this method to study areal and angular distortion. This method is particularly useful when analyzing large geographical extents (such as in global climate studies) where distortions are significant, as well as visualizations for which information is geo-referenced and perhaps scaled to the underlying map. It serves as a reminder that distortions exist in maps and provides information about the degree, location, and type of distortion.


This paper entitled: Floating Ring: A New Tool for Visualizing Distortion in Map Projections was presented at the CGI'98 conference and is available by clicking here , or by anonymous ftp to then get pub/reinas/papers/

An expanded paper describing the interactive map projection system and the distortion rings in both 2D and 3D will be published by Computers and Geosciences. A preprint version is available here.

Educational Software for Map Projections

The following map projection software is publicly available as long as it is not used for profit, and acknowledgements should be made to University of California and to the USGS. The software is written in C++. OpenGL is used for graphics rendering, while FLTK is used for the graphical user interface. The actual coordinate transformations are done by the GCTP package from USGS .

Windows and NT versions:

Executable 315kb
Coastline data . 1.2mb

Sun Solaris version:

Executable 1.3mb
Coastline data . 485kb

SGI IRIX version:

coming soon... XXXmb
Coastline data . 485kb


The program supports three general forms of map projections -- conical, cylindrical, and planar. It provides a graphical user interface for the user to select the type of projection and other parameters. Since the coastline is quite large (485kb binary or 1.2mb ascii) and can slow down the rendering, the user can hide the coastline until a desired mapping has been selected.


The Globe Window

Shown is the globe with coastline, and a cylinder as the geometric shape, indicating a cylindrical projection will be produced.

The Projection Window

Shown is the Wagner VII projection, a pseudo azimuthal projection. The cyan colored ring is the Floating Ring, which appears distorted from its original circular shape (on the globe) in both size and shape.

Conic Projection and Floating Ring

Parts of the Globe and Projection window are shown. The red cone is an interactive visual tool that indicates a conic projection, shown at right (Albers Equal-Area Projection).


Please send us your feedback, comments, suggestions, etc. Also send us email if you want to be notified of upgrades.

Related Sites:

Return to AVIS home page.