Source: Boundaries were derived from
several composite maps in United States Geological Bulletin 1212 by
Franklin K. Van Zandt, published by the U.S. Government Printing Office,
Construction: Sometime in the 1970s I traced separate maps for each year involving a boundary change. Around 1987 I digitized those maps and wrote a BASIC program to display them (on a Mac Plus, I think). Today (13 Jul 96) I modified the program (for simple color), downloaded screen images, used GraphicConverter to trim and color them, then GifBuilder to construct the animated gif.
Display: The animation begins as the page is called up. Once cached, re-displaying the page (e.g., via the button below), should produce boundary changes with a time-delay of one second.