Well, actually, there is a more accurate depiction of the siren system from Marion County Emergency Management. The siren coverage you display don't seem to stretch far enough. The actual depiction of Indianapolis shows that almost all the sirens inside I-465 overlap with others, creating a great system of sirens with no coverage gaps. Here is the thread started on the old forum which will soon include the surrounding counties of Indianapolis (starting with Hamilton County I believe):
http://www.airraidsirens.com/board/view ... sc&start=0
A current map with added siren locations with a color key (courtesy of Matt Heckler - caution large file size):
http://img.photobucket.com/albums/v63/q ... n4_new.jpg
I have the actual PDF of the system before Marion County took it off their website during an upgrade. I'll go hunting through my data CD's to pull it up. Once I do, I'll post it.