Thread: OneIndia Satguide INDIA STREET MAP 628 Cities Map update 28April10 -Garmin

You will have to enable/disable manually since the GPS unit is not aware of what you describes as more details, only the priority of the map.
Map drawing is only prioritized first by map priority (highest) and then by mapID (lowest). The device doesn't calculate what map has most details and give that map some preferred drawing priority.

I'm not acquainted with the map capabilities of a nüvi 200W. Normally the GarminDevice.xml gives some clues about map paths and names.
Most units can have "gmapbmap.img" (basemap), "gmapprom.img" (primary pre-installed map), "gmapsupp.img" (supplementary map), "gmapoem.img" (normally OEM POIs), "gmapprom1.img" (secondary pre-installed map) and "gmapsup2.img" (secondary supplemental map).
It's also possible to merge IMG map files with GMapTool into one IMG file.

Read more in the threads provided here:
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[Only registered and activated users can see links. ] - might give an indication of similar capabilities for a nüvi 200W