Google-maps – How to tweak the Google Maps app to display polygons/markers based on zoom level

I've created a hideous and slow Google Map at:

http://test.barrycarter.info/gmap4.html

The markers represent temperatures at given locations, and the
polygons represent a Voronoi diagram of the temperatures (sample data:
not accurate).

Question: is there something Google Maps API can do automatically to
display less information at one time? For example, not displaying all
the markers or every single polygon, even the really small ones?

I realize I could tweak my app to display polygons/markers based on
zoom level, but is there a way to make Google Maps API do the work?