Problem with sharing URLs is that people would be able to zoom in and see exactly where the messages/echoes come from. Not all of our users would be comfortable with that.
If they've just seen an accident, they'll want to post a URL. If they're at home, not likely.
You might even ask users to "mark" private locations from which location can't be sent, like school, home, or work.
You could also allow the user to vary the accuracy of the position by zooming in/out, to give them control of proximity for their posted locations.