Some sources of base data:
Try pasting the following KML code into My Places in Google Earth. It will produce the crosshairs screen overlay we demonstrated in the session. For more on creating and editing legends, logos, banners and screen overlays, see the Google Earth Outreach training site.
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<ScreenOverlay>
<name>Simple crosshairs</name>
<visibility>0</visibility>
<description>This screen overlay uses fractional positioning to put the
image in the exact center of the screen</description>
<Icon>
<href>http://developers.google.com/kml/documentation/images/crosshairs.png</href>
</Icon>
<overlayXY x="0.5" y="0.5" xunits="fraction" yunits="fraction"/>
<screenXY x="0.5" y="0.5" xunits="fraction" yunits="fraction"/>
<rotationXY x="0.5" y="0.5" xunits="fraction" yunits="fraction"/>
<size x="0" y="0" xunits="pixels" yunits="pixels"/>
</ScreenOverlay>
</kml>