The Google Maps API is probably the most popular of the mapping APIs right now. There is a good reason for it, the API is intuitive and fairly comprehensive. The performance is excellent and the quality of their data seems to be quite good.

To begin using the API, the developer must first get a key from Google here. The API reference is here.

I had no real challenges using the API other than the fact that putting a Google Map in a hidden div tag seems to cause some problems.

NOTE: With the new version of Virtual Earth just released, they have a new control for switching map type, navigation, etc. This appears to be a little buggy, I notice the map type (aerial, street, hybrid) is not on the control in FireFox. I'm hoping this will be fixed soon.

The Virtual Earth SDK is a close second to Google as far as popularity, and gaining. As is for Google, the SDK is intuitive and fairly comprehensive. The performance is excellent and the quality of their data seems to be quite good. One of the great things about Virtual Earth is we do not need a key. We can just start using the SDK simply by adding the Jacascript link to the map control. All done.

An excellent tool to use is the Virtual Earth interactive SDK here. This allows us to create a map in a Virtual Earth control, then simply copy and paste the code to our application. Developers can also download a CHM of the SDK to their desktop, which makes looking up reference information much easier.

I had no real challenges using the SDK other than the fact that putting a Virtual Earth Map in a hidden div tag seems to cause some problems. Of the maps, I feel that Virtual Earth needs to work on their symbology a bit. The map is too cluttered with text and features that should be more visible do not "pop". The map colors are very muted.

The Yahoo! Maps API can be a little confusing an overwhelming at first. There are multiple API offerings, including: "Yahoo! Maps Simple API", "Yahoo! Maps Flash APIs", "Yahoo! Maps AJAX API" and "Map Image API". There are multiple flavors of the Flash APIs as well. I know there are developers out there that will like having so many APIs available, but personally, I find it annoying. I decided to go with the AJAX API. I started out using the Flash API, but the map had problems refreshing on the client, especially in FireFox. We have to request an application ID to use this API, similar to the key request from Google Maps.

More information can be found here.

Yahoo! Maps had very few challenges. I have to admit that I am not exactly keen on their Flash maps API, I found the AJAX API much easier to work with. Yahoo! has done an excellent job with their mapping. The symbology is nice, the colors are excellent and the maps have a good look in general. Of the maps, I feel this is the best aesthetic-wise.

Click here for the ArcWeb Explorer Javascript map.

Why isn't the ESRI map here?  ESRIs mapping solution uses Flash.  Unfortunately, Flash has proven to be a problem with the other mapping APIs and with AJAX.  Therefore, I was unable to provide it as a tabbed map.  But, if you click on the link, it will open in a new window.

Lucky for us, ESRI will be coming out with a new solution with the release of 9.3.  This solution will use ArcGIS Server services.  I cannot wait for this!  Maybe we will get some real GIS out of the APIs now...

ESRIs current solution is the ArcWeb Explorer Javascript API.  Some of the things I liked were the widgets are very nice and I can use real map scales (1:50000) instead of "zoom levels".  When finding addresses, I found that ESRI's and Google's coordinates were a very close match...interesting.  Also, ESRIs imagery seems to be better then the others.  The only downside I saw was their use of Flash.

To get started, you will need to get a ArcWeb Public Services account here.  Next, go to the ArcWeb Explorer Javascript page here.  You do need to sign up for keys, similar to Google and some of the others, but one thing I liked is one key can be used on multiple sites (prod, dev, etc) as long as you register the URLs.  Finally, the API can be found here.

Click here for the MapQuest OpenAPI map.

Why isn't the MapQuest map here?  There are a few reasons, all can be read about in the "About this application" link found above, in the "Challenges" and "Other APIs" sections.  In general, MapQuest doesn't agree with the other mapping APIs or AJAX very well.  They also do not have a way to switch map views in the API (i.e. - aerial photo view).  I do provide the link for you to open the map in a new window and test it out.

I found this API the most difficult to work with; it was not intuitive or developer-friendly, IMO.

Information about MapQuest's OpenAPI can be found here.