The problem with the crown seems to be that it's not easy to pan longer distances like with pinch and zoom. You have to zoom out using the crown, pan across by swiping, and then zoom in again with the crown.
I'm a developer of a map app and I have added a panning gesture that only requires one touch of one finger. Admittedly the finger gets in the way whilst touching, but one finger is less obstructive than two. And one touch is a lot easier than the multi-touch gymnastics of pinching.
Basically you press and hold with one finger. After a second (so it knows it's not a tap) the map begins to zoom out. The original area is shown with a box around your finger. When you get to the zoom level you want then you move your finger and position the box over the area that you wish to pan to. Let go and it zooms back in to that area. If you move to the edge of the screen then it auto-pans across in that direction.
It's actually a lot more simple and intuitive than it sounds. When I show people they are usually surprised it hasn't been thought of before (although maybe it has been, but isn't used for some reason).
It's also good for showing what area you are looking at, which is particularly useful on a very small screen. You don't need to move your finger when it is zoomed out, so just tapping and holding zooms out to show the surrounding area. When you have zoomed out far enough to know where you are then let go and it zooms back to where you started.
I don't know how effective the gesture will be on a watch screen - I guess it depends on the relative sizes of your finger and the screen. It doesn't replace pinching or zooming for operations where you actually want to change the scale, but is simpler for when you just want to see the area around where you are looking at, or want to pan to a different area but at the same scale.
It's not just for maps either. For example it could be useful when editing an image or reading a pdf on a screen that is too small to show the whole document.
It's described in more detail here if you are interested, along with a video of it in action in a very old and embarrassingly bad version of the app.
http://www.poison-maps.com/Gestures.html