[GPSNavX]

My experience with raster charts is sometimes the smaller scale chart has a detail the larger scale has and as such I don't want the app to automatically decide for me to show the larger scale. Also most raster charts have important information in their borders, the apps that attempt to stich them together seem to crop this info out.

iNavX shows the larger scale charts as red outlines on the smaller scale viewed chart. Tapping the inside the red outline will display a menu where the larger scale chart can be selected. Also the "+" and "-" buttons on the raster chart allow a larger or smaller scale chart to be selected.