if you look at this post
[Only registered and activated users can see links. ]
you'll see that:
gmapbmap.img - garmin Base map you must have it in your garmin folder if you dont have it yet
gmapsupp.img - Secondary Map is your china map , it's your second map you must rename gmapsup2 to see them both

CHNNVENG.JCV is 3D-Buildings, Lane Assistant but it works just on Garmin nüvi765W, nüvi205(W), nüvi255(W)(W+), nüvi260W, nüvi760, nüvi200 (with CH Firmware 3.6), nüvi200W (with CH Firmware 2.9)

the guide i was speaking about is this one
[Only registered and activated users can see links. ]