Try searching for accumulation buffer antialiasing. OpenGL ES (WebGL) doesn't directly support an "accumulation buffer" the way desktop OpenGL does, but you can emulate it with render to texture and appropriate blending settings.

Now that I think about it, it may not work as well for your app as Google Maps. The thing about Google Maps is that when you zoom or pan the map the whole screen moves. In your app when you drag something, everything else remains static. The static items on screen will flicker between aliased and smooth whenever you drag something else. That will be distracting.