GRIDS and Graticule

[François TOURDE]

Hi,

I don't undestand clearly what is the exact signification of these
GRID parameters.

#      MINARCS 4
      MAXARCS 10
      MININTERVAL 1
      MAXINTERVAL 15
#      MINSUBDIVIDE 1
      MAXSUBDIVIDE 2


Could somebody explain me what's an ARC, what's a Subdivide, and,
cerise sur le gateau, how MAPSERVER (or me) choose the best interval
for displaying Graticule?

Many Thanks