Using a Scale on an OpenStreetMap Map
You need to show a map scale on your OSM to indicate the level of zoom on the MapView
A scale can be added on the OSM as an overlay using the ScaleBarOverlay class
Putting a scale on your MapView helps the user keep track of the zoom level at which he is (also helping him/her of the approximate distances on the map). To overlay a scale on your OSM MapView, instantiate the ScaleBarOverlay and add it to your MapView using the add method.
Here is how the code would look:
ScaleBarOverlay myScaleBarOverlay = new ScaleBarOverlay(this);
The scale bar overlay looks like this: