The Itinerary Of The Blue Khan...

Carl Cheng, Santa Monica Art Tool (1988)
http://we-make-money-not-art.com/archives/
2010/08/the-map-as-art-contemporary-ar.php#.UKHEiOSw8TY

...tracing his spherepath through the realms he destroyed. The Blue Khan came from Beyond the Deep Horizon. When settlers from the First City made their journey toward Otherway, they found the ruins of a number of recently destroyed realms along their way. These realms had been conquered, looted, and subsequently uprooted and erased by the Blue Khan.

A frequent metaphor for The Blue Khan's itinerary of annihilation among the spheres is the "roll over": his armies completely rolled over and erased numerous realms. In some cases, the ruins are still visible, and indeed some religious pilgrims seek out these worlds as sites to found monasteries and centers of meditation. Potent wizards also seek them out in an effort to catch Radiance left behind by the Blue Khan, his creatures, and his armies.

Still other realms are completely missing: the ancient gates leading to these realms no longer work, and these worlds are lost forever. However, impressions of them linger ghost-like here and there. For example, traces of them can be found in the small roller-charms called the Itineraries of the Blue Khan. These are miniatures of the larger vehicle-drawn rollers that the Blue Khan's armies used to crush and flatten the cities of his enemies. 

The large rollers took an impression of the realm they destroyed. They took into themselves the history and geography of those realms. The large roller's records could be transferred to smaller roller-charms, as well as "printed" as it were on large sandy areas. However, once one of these terrible roller weapons went through a gate, the information pressed under and impressed onto its great crushing wheel (as shown in the picture, above) was erased for all time. 

The good news is that the small roller-charms are persistent records that can be used to make maps on sand tables, or to print record strips on long rolls of paper. The ghost impressions formed by the roller-charms are our best record of many of the now-lost realms, and of the gatepaths between these realms and others. As such, they are highly prized by scholars seeking understanding of lost connections between worlds, as well as by certain vengeful hunters searching for any trace of the Blue Khan and his armies. 

Reports that a series of these roller-charms can also be assembled into a Gate Generator have not been confirmed.