In 2010 I went to South America. I had with me the 255W and I used some maps from a guy names smellybiker, he has some sort of subscription based maps. I don't know how I ended purchasing that but I wasn't quite happy because map was not so accurate.
This time I was looking to try something else.
I have 2 Nuvi 255w units.
one has sowftware worldwide autoroute dem basemap 5.00 with "CN Nort America NT 2011.10  US & Canada" map
the other one runs worldwide autoroute dem basemap 3.00 with "CN Nort America NT 2010.10  All" map
on both I browsed some asian countries and I saw only motorways displayed. No streets, local roads etc.
My experience with GPS systems and Garmin in particular is VERY limited so I was trying to find out which is the most effective (yet not too expensive) way to have decent road and geographical info for Asia.
Currently I only have the GPS receiver and cable, nothing else.
Your nuvis only have Garmins basemap, which is why you only see the barest details. I have no idea I'm afraid about maps for Asia, never having been there, but have a look at sites like OpenStreetMap for free maps. The alternative is maps like this from Garmin:
The solution is to either buy the appropriate map on SD card from Garmin or buy a new GPS in the area of the world you're going to when you get off the plane.
Garmin markets different versions of the GPS in different parts of the world for a good reason - to reduce costs. Maps cost money and including detailed maps for the entire world would raise the price to several times what it is now as well as making it necessary to have much more map storage memory on the unit.
The best source of compatible maps will always be the original GPS manufacturer. You pay for quality but it's well worth it in my opinion.
Bob Peloquin - Moderator-Lowrance iWay forum Massachusetts, USA Various Iways, nüvi 750