http://code.google.com/apis/kml/documentation/mapsSupport.html tells
us that Google Maps API limits us to 1000 “Maximum number of total
document-wide features”.
I interpret this to mean 1000 polygons (for example) *total*,
regardless of zoom level.
They’re actually usually more generous: http://wordpress.barrycarter.org/index.php/voronoi-temperature-map/ routinely loads 3000+
polygons without any problem.
The limit also only applies to polygons on the visible map, not the
whole map: when I briefly modified the page above to have 6000+
polygons, Google only rendered some of them, resulting in this cool
“shattered glass” effect:
Once I zoomed in a little, everything was fine:
