Click on the Start up 
node under your MyMaps MapSource entry.
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Here you can configure the startup information for your MyMaps Map Source.
Startup Position
Enter the details for the Startup Zoom level and Easting and Northing coordinates.
Boundary Settings
Here you can set the co-ordinates for the Maximum Bounding Rectangle (MBR) to prevent users moving outside the specified area. Enter the MinX, MinY, MaxX and MaxY co-ordinates for your map boundary.
Zoom Settings
Enter the Max Zoom and Min Zoom to set the maximum and minimum overall zoom for the map.
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