change radius by zoom level
<p>I wish to calculate radius in meters or km according to the zoom level.</p>

<p>I've found this formula - which gives me the roughly calculated meters per pixel:
<a href="https://groups.google.com/forum/#!topic/google-maps-js-api-v3/hDRO4oHVSeM" rel="nofollow noreferrer">https://groups.google.com/forum/#!topic/google-maps-js-api-v3/hDRO4oHVSeM</a></p>

<p>Also, these links assisted me in understanding what I was trying to accomplish exactly:
<a href="https://stackoverflow.com/questions/9356724/google-map-api-zoom-range">google map API zoom range</a>
<a href="https://stackoverflow.com/questions/13904505/how-to-get-center-of-map-for-v2-android-maps">How to get center of map for v2 android maps?</a></p>

<p>and this is the implementation:</p>

<pre><code>double calculateScale(float zoomLevel, LatLng centerPos){
    double meters_per_pixel = 156543.03392 * Math.cos(centerPos.latitude * Math.PI / 180) / Math.pow(2, zoomLevel);

    return meters_per_pixel;
}
</code></pre>

<p>and this is how I listen to the zoom level changing:</p>

<pre><code>        _map.setOnCameraIdleListener(new GoogleMap.OnCameraIdleListener() {
        @Override
        public void onCameraIdle() {
            Log.d(Consts.TAGS.FRAG_MAIN_MAP,"Current Zoom : " + _map.getCameraPosition().zoom);
            Log.d(Consts.TAGS.FRAG_MAIN_MAP,"Center Lat : " + _map.getCameraPosition().target.latitude +
                    ", Center Long : " + _map.getCameraPosition().target.longitude);
        }}
</code></pre>

<p>Now, whenever the user changes zoom level, I wish to determine what is the maximum radius that can be displayed within the map view...</p>