Today I'm going to talk about image overlays for Google Earth. Google Earth, as you may have heard, is the latest iteration of the Keyhole application, which composites archived satellite images of anywhere on Earth together and streams them to your computer so that you can at will pan and zoom around the entire world. And, image overlays are nothing more or less than arbitrary image files which can be pasted down on top of the satellite imagery. These images can come from your local drive, or they can be fetched from any URL on the World Wide Web. And what that means, of course, is that whenever any website offers a constantly updated image for download at the same URL, you can paste that image onto your Google Earth and see it updated in real time whenever you want.
To make an image overlay, you select the option to add an image overlay from the menu; you browse or enter the image location in the dialog box; you drag the handles on the image so that it's correctly placed on the globe; you request an auto-update every so often; and that's it, really. For example, I made this overlay to deliver tomorrow's weather forecast properly overlaid on the central United States. (Note that it's just a tiny little file too, only 612 bytes.) There's nothing to it at all -- try making one yourself!
And once you have done so, ponder that this is basically the "Earth" application as seen in Neal Stephenson's cyberpunk classic Snow Crash.