Make google maps fit a radius and pos - based on http://www.movable-type.co.uk/scripts/latlong.html

fit-map.js

function toRad(num) {
    return num * Math.PI / 180;
},

function toDeg(num) {
    return num * 180 / Math.PI;
},

function destinationPoint(LatLng, bearingDegrees, radiusMeters) {
    dist = radiusMeters / 1000 // convert to KM
    dist = dist / 6371; //Radius of earth approx
    bearingDegrees = this.toRad(bearingDegrees);

    var lat1 = this.toRad(LatLng.lat()), lon1 = this.toRad(LatLng.lng());

    var lat2 = Math.asin(Math.sin(lat1) * Math.cos(dist) +
        Math.cos(lat1) * Math.sin(dist) * Math.cos(bearingDegrees));

    var lon2 = lon1 + Math.atan2(Math.sin(bearingDegrees) * Math.sin(dist) *
            Math.cos(lat1),
            Math.cos(dist) - Math.sin(lat1) *
            Math.sin(lat2));

    if (isNaN(lat2) || isNaN(lon2)) return null;

    return new google.maps.LatLng(this.toDeg(lat2), this.toDeg(lon2));
}

function extendMapToFit(map, pos, radius){
    var center = new google.maps.LatLng(pos.lat, pos.lng);
    var bounds = map.getBounds();
    bounds.extend(destinationPoint(center,  90, radius ));
    bounds.extend(destinationPoint(center, -90, radius ));
    bounds.extend(destinationPoint(center, 180, radius ));
    bounds.extend(destinationPoint(center,   0, radius ));
}
}