Ah, nothing like a new trick that makes using Google maps just thaaaat much easier. Carl Sednaoui and a friend discovered a new "secret" gesture for Google Maps for iPhone that allows you to zoom into a map with just one finger, so you don't have to have both hands on your iPhone in order pinch and zoom.
He writes, "To perform a one-hand zoom simply double tap on your map and, after the second tap, leave your finger pressed. You can then move your finger up and down to zoom in/ zoom out."
He has an animated gif showing the feature, but of course you could just try it out on your device. It didn't work when I tried it on my iPhone (double tapping zooms in, in increments) but I might just need to update my app. Let us know if it works for you!