How to add Google Map in windows phone app

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C#

Windows

Google-Maps

I am very new to the development ground, and I am developing an app which uses Map service. I am developing that app for Windows Phone 8.

I followed a link http://themightyhedgehog.blogspot.de/2013/01/how-to-use-google-maps-in-your-own.html and tries to develop an app containing Google Map.

But I got an error in Xaml on line MapAppScope:BindingHelpers.TileSource="{Binding GoogleMap}"

and the error I got are:

BuildingHelpers is not supported in Silverlight.
The attachable property 'TileSource' was not found in type 'BuildingHelpers'.
The Namespace prefix "MapAppScope" is not defined.
So please can anyone helps me to do the needful.