Read original post by Joost van Schaik at .NET by Example
The Bing Maps control in Windows Phone 7 is pretty versatile but does not always play along very well with data binding. You can bind ZoomLevel and MapCenter, which is all very well, but if you want to know what area is actually shown within the map – for instance, for making a GIS application that loads only visible data, and not stuff that’s outside the view area anyway, things get a lit complicated.
Not so if you uses this little behavior. It builds upon the SafeBehavior that is already in my wp7nl library on codeplex. It sports two GeoCoordinate depencency propertise, NorthEast and SouthWest [...]