Mobile local search is obviously one of the biggest opportunities for Internet search companies like Google, Yahoo, and Microsoft. According to this New York Times article:
“The biggest growth areas are clearly going to be in the mobile space,” Eric E. Schmidt, chief executive of Google, said when asked about new opportunities at a conference here this week. In case his point wasn’t clear, Mr. Schmidt drove it home: “Mobile, mobile, mobile.”
Well, I have been using both Google Maps and Yahoo! Go for some time. They are both excellent J2ME applications. Here are some of my thoughts:
What I like about both apps
Both Google Maps and Yahoo! Go are very usable mapping applications. They can find locations by address or business names (even incomplete ones), display area map, support multiple levels of zooming, and support easy scrolling / panning. Leveraging the multi-thread mobile application runtime, they both fetch new map images tiles in background -- and hence they are much more usable than displaying static maps on a mobile web page.
Local business search is built into both applications. When you enter a search phase, the application searches for businesses in the vicinity of your current location and marks the business locations on the current map. You can then access information of those businesses by pressing the corresponding number key. You can call any business from the app if it has a phone number listed. You can get driving directions to/from that location. You can also see reviews and ratings in Yahoo! Go.
The turn-by-turn driving directions are handled very well on both applications. You can view each turn instruction with its corresponding map like a slide show -- using your keypad to navigate to the next/prev turn. The experience is quite like having a real GPS in your hand.
What I like about Google
While Google Maps is not full screen (this seems to be a big oversight), it manages to display maps in finer details than Yahoo (see below). I think high map resolution is crucial for mobile phones -- it reduces the need to zoom in and out just to see a street name. Somehow, the maps from Yahoo! Go look very clumsy on the mobile and there are too few street names on the Yahoo Map -- you have to zoom really close to see the street name and then zoom back out to see the overall area.
Typical Google Maps:
A typical Yahoo map:
Google Maps is more stable than Yahoo! Go. The Yahoo application occasionally freezes if you try to do too many things too quickly (it even freezes if you try to zoom too quickly). That is highly annoying on a mobile phone. I almost never encountered a freeze on the Google application.
The overall workflow of Google Maps is also more efficient than Yahoo! Go due to the support for "saved" locations. In Google, you can save any address (or search result) in a "favorite" list. You can then go to any saved point directly to view its surrounding map, get driving directions to/from it, and search businesses / locations around it. When you select a search result anywhere on the map, you can also easily choose a location from the favorite list to calculate the driving directions. It is very useful if your trip has several stops. Yahoo, on the other hand, do not provide an easy mechanism to save locations temporarily. You can only save Yahoo locations on the Yahoo web site and then access the saved list from the phone. That quite severely limits the usefulness of the mobile client. Of course, Yahoo has a very nice "auto-completion" feature in its input box that makes finding previous locations a little easier (see more on this later).
Google Maps makes better use of the numeric keypad to provide quick access to saved address lists, search results, driving directions, zooming, and other important menu functions. Yahoo! Go requires you to use the softkeys (or the joystick) to navigate, which is just a lot slower than shortcut numerical keys.
Google Maps provides satellite images as well as street maps. I find that quite useful when the streets are confusing. Yahoo does not offer that feature.
Mapping applications are bandwidth intensive. I can easily consumer more than 1 MB of data in one day while I am on a trip. The kilobytes gauge on Google Maps is useful when you are on a metered Internet connection. It allows you to see how much bandwidth you have consumed in the current session. It would be nicer if the bandwidth gauge is saved in a persistence storage and collect data across different sessions.
What I like about Yahoo
Now, you might think that I like Google Maps much more than Yahoo! Go. But that is far from the truth. 
Mobile applications are like icebergs -- they are 10% mobile UI and 90% server support. IMO, the strong point of Yahoo! Go is its tight integration server services. In contrast, Google leverages little server services other than geo-coding, map rendering, and local business searching.
Yahoo! Go incorporates a complete Yahoo search engine. You can search any term and get a list of businesses / locations back. You can view the details of each search result including its ratings, reviews, or even go to its web site -- Yahoo! Go reformats the web site and fits it into your mobile screen. Google, on the other hand, offers a much less sophisticated local search engine. When you enter a search term in Google, it just marks the returned locations on the map. Each Google location only has an one-line title. It is sometimes woefully inadequate -- I tried to search for USPS post offices on Google Local Mobile: it returns some shipping supply shops and USPS pickup locations, but gives me no way to tell which one is the real post office.
In addition, Yahoo! Go integrates personalized news, stock quote, email etc. from your Yahoo account all into one application. Of course, that is beyond the scope of a "mobile map" application but I find the highly integrated user experience very appealing.
Besides tight server integration, Yahoo! Go also offers several mobile UI features Google lacks: The Yaoo app is full screen -- very important for mobile phone apps. The text input box in Yahoo! Go remembers all the phrases you typed in the past and offers auto-completion suggestions as you type.
The verdict
I guess the bottom line is that I liked both applications. I find myself using Google Maps more often while I am driving / walking around since it has better maps. But when I am at a place and try to plan the next destination, I almost always use Yahoo! Go to take advantage of its better search features.
