I've tryed Google Maps.
Yes, it is possible to import my *.klm file there and yes, it is easy
to edit it (I wish I have the same in Google Earth). But how to export
the edited map back to my local computer? I tryed to do this using
link "Show in Google Earth" and I saved the exported *.kml file to my
disk and I can open it using Google Earth. But it is completely
different file! Instead of set of a polygon's coordinates I have just
a link now!
So, the question is still open: is there way to edit the existing maps