The Envelope for the InitialExtent is what is provided by the ArcGISLocalTiledLayer. It should be noted that depending on the aspect ratio (i.e. Height and Width) of the Map Control, that what is viewable on the screen for the ArcGISLocalTiledLayer could be different than the published InitialExtent when the application first loads. The reason for this is that ArcGIS Runtime attempts to center the map based upon the extent and maintain the scale subject to the Data View when the package is initially published from ArcMap. If it is desired to specifically set the Extent of the Map Control to be exactly the ArcGISLocalTiledLayer.InitialExtent, set the Map.Extent to that ArcGISTiledMapServiceLayer.InitialExtent in the code-behind.