The blogosphere only talks about Google Maps today. I've looked at it, and feature-wise, I'm not that impressed.

For years, I've been using Mappy which provides the same and more with a very friendly and reactive Flash-based GUI. And in some locations, Mappy also provides aerial photographs . In the "Maps" menu, select "Aerial photos" and click on a town of your choice. You can then play with the top-left "transparency" slider to see what I mean.

Now looking at the technical details of Google Maps reveals an impressive architecture: display a map, and have a look at the page info in Firefox (under the "Tools" menu). No Flash at all, it's all Javascript+bitmaps.

The map is actually a set of tiles, which have URLs like " http://mt.google.com/mt?v=.1&x=-2370&y=-1045&zoom=3", i.e. geographic coordinates and a zoom factor (what is the "v" for?). Signs that come on top of the map use transparency to render nicely. The only dynamically produced images are actually the path corresponding to your particular request.

What that means is that Google can replicate the statically-generated map tiles all over it's worldwide filesystem, and that if you often query the same area, it's likely that the map images will already be loaded in your browser cache or in your company's/provider's proxy cache. Clever.

But I'm wondering if more advanced interactive features can be provided with this JS+bitmaps architecture, which are easy to provide with Flash or SVG.

Anyway, the Google peeps know how to use at its best the rich client features that today's browsers provide. Well done.