Creating the Apple Lisa (and Mac) user interface

How exactly are graphical user interfaces (GUI) created? Obviously it involves quite a lot of advanced programming and design work but where do you start, especially back in the 1970s when there weren't many examples of GUIs to gain inspiration from? This extraordinary page on the Mac Folklore website has a series of photographs how the Apple Lisa GUI developed from the first basic graphic tests to the finished article which shipped in the early 1980s, and later carried on by the Apple Macintosh to the present day.

What is especially interesting how the Apple UI, with elements still familiar and used today such as the menu at the top, evolved. Early in the Lisa GUI development a softkey menu along the bottom of the screen was the direction the developers took before the abrupt change to a window and mouse based design. Inspired / stolen from Xerox PARC? Well various theories abound, i'm sure there was plenty of inspiration taken but some elements of the GUI are said to predate that.

It is interesting that in 1980 the Lisa had a menu on the top of windows (like Microsoft Windows later went with) instead of along the top of the screen as how the final design used.