If you have all of "SatGuide ONE INDIA, April 2010", "MapmyIndia v4.01" & "City Navigator India NT 2010.20" installed it will show and use the map with the highest priority for that area on your GPS screen. If they have the same priority it depends on how the device loads the maps in a sequence and it may vary.
One can have multiple maps for the same area and choose to disable/enable the ones in the settings depending what's best for the occasion or the narrow smaller region.

Priority 24: "SatGuide ONE INDIA, April 2010" & "MapmyIndia v4.01"
Priority 30: "City Navigator India NT 2010.20"