Regarding how to define lat/lon for a movie, see the online documentation for examples: http://www.ammap.com/docs/v.2/data/movies

Now, about defining bounding coordinates for a custom map... If I don't use GIS to create my map, I use one of the online map services (Google, Yahoo, etc.) to find the lat/lon coordinates the best I can. Then I use trial and error to refine the coordinates.  Good luck!