Code.aspx
<cc1:GMap ID="GMap1" runat="server" />
<asp:Button ID="Button1" runat="server" Text="Click Me" />

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Code.aspx.cs
GMap1.addControl(new GControl(GControl.preBuilt.LargeMapControl));
GMap1.addControl(new GControl(GControl.preBuilt.MapTypeControl));

GLatLng latlng = new GLatLng(42.12, -1.145);
GMap1.setCenter(latlng, 5, GMapType.GTypes.Hybrid);

GMap1.addGMarker(new GMarker(latlng + new GLatLng(2, 1)));