In rcParams we can control the number of symbols for a normal plot with
legend.numpoints : n
I suggest that we add a new key
legend.scatterpoints : n
That fills in the value for:
This is already marked as TODO in the code ( https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/legend.py#L138 ) and is already implemented except for adding the default values.
Resolved in #1634.