procedure TForm1.ZoomToFit;
var
  maxCoord: TTMSFMXNativeMKMapLocation;
  minCoord: TTMSFMXNativeMKMapLocation;
  coord: TTMSFMXNativeMKMapLocation;
  I: Integer;
  rgnm: MKCoordinateRegion;
begin
  maxCoord.Latitude := -90;
  maxCoord.Longitude := -180;
  minCoord.Latitude := 90;
  minCoord.Longitude := 180;

  for I := 0 to TMSFMXNativeMKMapView1.Annotations.Count - 1 do
  begin
    coord := TMSFMXNativeMKMapView1.Annotations[I].Location;
    if coord.Longitude > maxCoord.Longitude then
      maxCoord.Longitude := coord.Longitude;

    if coord.Latitude > maxCoord.Latitude then
      maxCoord.Latitude := coord.Latitude;

    if coord.Longitude < minCoord.Longitude then
      minCoord.Longitude := coord.Longitude;

    if coord.Latitude < minCoord.Latitude then
      minCoord.Latitude := coord.Latitude;
  end;

  rgnm.center.longitude := (minCoord.Longitude + maxCoord.Longitude) / 2;
  rgnm.center.latitude := (minCoord.Latitude + maxCoord.Latitude) / 2;
  rgnm.span.longitudeDelta := maxCoord.Longitude - minCoord.Longitude;
  rgnm.span.latitudeDelta := maxCoord.Latitude - minCoord.Latitude;

  TMSFMXNativeMKMapView1.MapView.setRegion(rgnm, True);
end;