Google maps api 3 如何使用overlayer在ios地图中绘制线

我想用overlayer在ios地图上画一条线。我有一个在地图上画线的代码。但这对我不起作用。有人能帮我吗

Mk坐标跨度； span.latitudeDelta=.03； span.longitudeDelta=.03

MKCoordinateRegion region;
region.span=span;
region.center=CLLocationCoordinate2DMake(39.046259, -76.851195);

[_myMapView setRegion:region animated:YES];
[_myMapView regionThatFits:region];

UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(singleTapWebView:)];
singleTap.numberOfTapsRequired = 1;
singleTap.delegate = self;
[self.myMapView addGestureRecognizer:singleTap];
[singleTap release];

CLLocationCoordinate2D commuterLotCoords[5]=
{
    CLLocationCoordinate2DMake(39.036399,-76.872208)
};
 MKPolygon *commuterParkingPolygon=[MKPolygon polygonWithCoordinates:commuterLotCoords count:5];
    [_myMapView addOverlay:commuterParkingPolygon];

在上面的代码中，我们可以从这行“CLLocationCoordinate2DMake（39.036399，-76.872208）更改终点，但在中，起点始终是 拉特0.000003，长0.000000。如何更改起始品脱。谁能帮我解决这个问题