You’ll need a jailbroken iPhone for this. But you’ve already done that, right?
Fair warning: I’m stuck with a first-gen iPhone, so I can’t personally verify that this works on any iOS past 3.1.3. Let me know how it works for y’all in the comments.
1. Search for a location/directions using Google maps on your computer.
2. Copy the link (using the “Link” button above the map)
3. Shorten the URL using bit.ly (or a similar shortening service).
4. On your iPhone, create a home screen button for any random sort of page you like in Safari.
5. SSH or use Netatalk to locate the new home screen icon in the iPhone. You’ll find it here:
(The titles are all gibberish, so either look through them all, or sort by date if you can to make it easy on yourself.)
6. Use a text editor to open Info.plist, and replace the web address with your new bit.ly address. Save and return to your home screen.
That’s it! The icon should launch Safari, which will then launch the maps app with your address or directions.
Now you only need one tap to show the address on the map, one tap to input your current location, and one more to calculate. If you used bit.ly to shorten directions from one location to another, a single tap will bring it up on the map, along with the next train or bus to get you from A to B.
(Why not simply enter the Google maps address into Info.plist? The link to google maps won’t work from the home screen like it does in the browser or email. The bit.ly link gets around this by calling up Safari to do the work.)
Hope this helps. Good luck!