I too have made this search and reached the same conclusions. It's also too bad that the Garmin world map doesn't indicate the Great Wall at all.
However, I did find some interesting alternatives (which I have not tried) and other information as follows.
http://mapcenter.cgpsmapper.com/mapl...=47&rgn=&cat=4
http://www.pda4x.com/read.php?tid=56398
http://www2.mapking.com/en/
http://english.people.com.cn/200602/...24_245682.html
It's also worth noting that Garmin GPS receivers sold in China via their partner Unistrong have more detailed and accurate maps which cannot be purchased outside of China.
http://www.unistrong.com/productline...de=GPSMap60CSx