It's been fascinating to watch the reaction of the geospatial community (and the non-geospatial community) to Google Maps.My sense is that because it's Google, there's more of a buzz, than say when Yahoo! Maps launched.That, I believe, has meant far more interest in the background technology and the general usability.It's also led to some interesting speculation about the technology behind the tool.

Google Maps is a combination of proprietary commercial technology (like that from Telcontar, which I wrote about earlier this week) and commercial data (from NAVTEQ and Tele Atlas) and some good old-fashioned, clever programming.Below is a quick look at that "clever programming piece" from a non-programmer and some clarification on speculation regarding technology that I ran into this week.

Technical Background
The key technical dissection of Google Maps appeared in a blog last week.Joel Webber took a look under the hood and highlighted some key technology decisions made by Google programmers.

First off, the application is built on DHTML.That's dynamic HTML and basically it means that a webpage is different each time it's viewed depending on different parameters.There are many ways to create DHTML, but Google Maps uses JavaScript.

Second, the map is tiled; it's a 128 x 128 grid.That explains why grid squares are painted.It's also what allows the unique scrolling that not available on other mapping portal offerings.

Third, the pushpins (the upside down teardrops that locate addresses) are transparent GIFs, but their shadows are PNGs.The shadows really have no place on the map, that is, there "geography" is not really relevant, but they to make the maps pretty and provide a pleasing 3D quality.They remind me of the line of scrimmage and first down lines available on TV during football games.They are not really "there," but help the viewer make sense of the geography of the field.

Fourth, the map is created by querying the correct tiles at the correct zoom level.(That reminded me of the GetMap query that's part of the Web Map Service specification from the Open Geospatial Consortium [(for whom I consult].) As these grid squares get cached locally, or perhaps elsewhere, it's suggested, panning and zooming get faster.

Finally, the map is separate from the search queries, meaning the entire page need not be redrawn each time a new query is made.

There's quite a bit more detail in Joel's overview.My point is that this is not some super fancy new thing.It's clever use of existing commercial tools and "Web stuff."

Some Apparent Misconceptions
Several articles I saw suggested the technology is built on Google's acquired Keyhole technology.In eWeek Marissa Mayer, Google's director of consumer Web products said "its technology was not directly used in Google Maps." That said, there's much speculation about how the two will be linked in the future.

Another comment suggested ESRI's ArcIMS was behind the solution.Thers is to date no evidence of that.Besides, if ESRI were behind it, I suspect we'd have seen a press release by now.That's not to say there is no relationship between the companies: ESRI count Google among its partners for the new version of geodata.gov.

One user in Canada "poo-poo-ed" Google since a small town of interest was not available via Google.The user noted that MapQuest failed to find it, too.But, Maporama did have it.That might be because the latter uses data from DMTI Spatial and I do not believe the others do. Another poster wanted to know how the data was updated.Google does not say, but data vendors do offer monthly and sometimes weekly updates for data.Few if any of the map portal vendors disclose how quickly they load those updates.Recall, too, that a change may take many months from its identification to its addition to a new dataset.

Add-ons Abound
One fellow has figured out how to transfer the area of interest from Google Maps over to Keyhole (trial or real version).It's a FireFox extension.Another has figured out how to add GPS data to Google Maps.Glen Murphy's website that illustrates how to hook a GPS up to Google Maps (Windows only, so far).From the Mac side, it's possible to integrate Google Maps into a Mac OS X Address Book.Some AppleScript Code adds a context menu accessible in the Address Book app.Right clicking on an entry will open a map of US address in the Address Book in FireFox.(Recall Google Maps runs happily on FireFox, which is supported on Macs.) Also for FireFox is a Google Maps searchbar. The amount of energy here is quite impressive.

Advertising on Google's Shoulders
Also of note, nearly every discussion (blog comments, newsgroups, etc.) of Google Maps I found included a reference to an online map service, Maps24 and how they are hiring.Nearly every one also had plugs for various online mapping services, worldwide hoping to get in on the excitement of the new Google offering.I suppose everyone wants to jump on Google's coat tails.