<UserControl x:Class="SilverlightApplication3.MainPage"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:esri="http://schemas.esri.com/arcgis/client/2009"
  xmlns:sys="clr-namespace:System;assembly=mscorlib">

    <Grid x:Name="LayoutRoot" Background="White">


        <esri:Map x:Name="MyMap" Extent="-120, 20, -100, 40" >
            <esri:Map.Layers>

        <esri:ArcGISTiledMapServiceLayer ID="StreetMapLayer"
          Url="http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_StreetMap_World_2D/MapServer" />
                <esri:GraphicsLayer  ID="MyGraphicsLayer" />

            </esri:Map.Layers>
        </esri:Map>

    </Grid>
</UserControl>