I have found these to be the best maps available in English and outside of China. The scale of these maps is 1:1,500,00.
Nelles Northern China Map - http://www.nelles-verlag.de/cms.php/...7/0/0/1498/0/0
Nelles Northeastern China Map - http://www.nelles-verlag.de/cms.php/_130294/1707/0/0/36/0/0
I have, however, noticed some errors in the locations of areas of the Great Wall on these maps.
Topographic maps of the Great Wall of China. These maps are 1:250,000 scale. They are the largest scale maps you will find with romanized characters. They have been scanned at a very high resolution. The Great Wall is clearly indicated on these maps.
Romanization is in the Wade-Giles system as opposed to Pinyin.
These maps have been released by the CIA. The maps are in the public domain and are not copyrighted. They are dated 1968.
Map sections are jpeg files of about 6 MB each. Maps are downloaded from the following two index pages. Printed maps are no longer available.
http://www.lib.utexas.edu/maps/ams/manchuria Maps NK-50-7, NK-50-11, and NK-50-12
http://www.lib.utexas.edu/maps/ams/china Maps NK-50-10 and westward from there.
These maps are available in Beijing and provide greater detail than any maps I have found outside of China.
Beijing city map (scale 1:290,000)
Example of the detail of the Beijing city map showing the Sanchakou area:
Beijing Self-Drive Tours map (scale 1:370,000)
This map includes a high definition (scale 1:370,000) map of the immediate Beijing area on one side, and a smaller scale (1:1,200,00) map of a larger area on the other side. Here is an example of the detail of the larger scale map showing Gubeikou, Jinshanling, and Simatai.