According to dictionary.com, reticulating
- To make a net or network of.
- To mark with lines resembling a network.
See also, Webster 1913's definition
. Therefore, reticulating splines
would imply making a network of splines
, not a single longer spline.
However Will Wright, the creator of Sim City 2000, has explicitly stated in an interview (unfortunately, so long ago I can't remember the source) that SC2000 does not actually reticulate any splines--the female voiceover was inserted because it sounds cool. If I had to guess, I'd say the landscapes are probably created using plasma cloud fractals, as most pov-ray landscapes are (see http://spanky.triumf.ca/www/fractint/plasma_type.html).