For anything more than an out-and-back day hike, it's a good idea to plan your hike before you go. This includes routing and logistics. The more lengthy and complicated your hike, the more important this planning in terms not only of successful completion but also safety.
Planning your route involves using a map to decide where you will go. This includes not only walking along the Great Wall, but any other hiking that may be necessary to get to and from the Great Wall, make your way around obstacles, and to walk in between spans where the Great Wall is not continuous.
This planning can be done on a paper map, especially a good, detailed topographic map that accurately shows the Great Wall. As we've already discussed, these maps are not easy to find, and people often wind up making their own maps. If you're going to the trouble to make your own paper maps then it only makes sense that your intended route would be shown on the map.
Alternatively, you can use online satellite imagery to plan your route. This solution has many advantages. One major advantage is the ability to transfer your route, and other elements of your map, to your GPS receiver to use while you are hiking. Your GPS will trace your path and allow you to compare this to your intended route. Route plans made on satellite images can be printed in various styles including satellite image, topographic, shaded relief, road maps, and the like. Once you get some practice in using satellite imagery to plan your route you will find the method practically indispensible.
Currently, the preferred application for working with satellite imagery is Google Earth. This program can be downloaded for free from http://earth.google.com. Once you have Earth installed on your computer, you can see much of the Great Wall as you view satellite images of the area. Use the path tool to plan your driving and walking routes. These paths can be organized into folders and saved as files. The files you create can then be used with Google Maps (http://maps.google.com in English or http://ditu.google.com in Chinese) for printing in the style of your choice. They can be used with a GPS receiver as well.