There is no real tutorial with the map scripts . But take a look at "CvMapScriptInterface.py" in the python entry points . All the function called with a map script are well described there .
Code:
* minStartingDistanceModifier() # Can increase or decrease (by a percentage) the standard values for minimum distance between any two start plots.
If you want more infos with default implementation of the map script you should take a look into the sdk ( especially CvMapGenerator.cpp , CvGame.cpp and CvPlayer.cpp ) . For the use of minStartingDistanceModifier() take a look at CvPlayer::startingPlotRange() used with the default implementation of CvPlayer::findStartingPlot() . If findStartingPlot() is overridden in your map script , minStartingDistanceModifier() have no use .
this function is usefull with map scripts where starting location are supposed to be closer than there size ... ex : Terra ( where all civ start on a half of the map ) , Hub ( where all starting plots may be very close compare to the size of the map ) , ...
Tcho !