The phrase "Cartographer's Nerves" refers to the feeling of being given an impossible task to do, for example, scrambling an egg while it is still inside it's shell, or walking and chewing gum at the same time. The phrase originates from an aside in Alarius' A Commentary on the History of History, Historio-Physis, and the People of the Bute, in which he describes the effect of the Bute founders' doctrine on the king as a cruel irony, reciprocal to the "Mapmaker's Trials" the king had presided over a year before the Bute scholars' problematic publication.
Discovering reality dissolving around him, and the castle literally changing form from day to day, Harandraff finally felt empathy with his mapmakers.
Alarius went on to develop "Cartographer's Anxiety" as the characteristic state of the entire "Primary Subject" period of history, a parallel to the attempt to enforce consensus realty by embodying the consensus in the historical location of a single monarch being parallel to the attempt by cartographers to assert positional relation before the fact, paradoxical not only in eliminating or subjugating existing historio-physical effects relative to the map reader but in that the act of exposure to a map in fact suggests to the reader geographical alternatives that then become relative realities. Alarius goes on to his famous conclusion that the surest way to hide a place is to draw a map to it.
The current clever example of Cartographer's Nerves in the Alarian sense is the role of the hunter in Timperton's thought experiment:
An aelfant is captured, and locked in an enourmous, opaque box, along with documents recording its capture. Later, its captor is drinking with friends, and mentions his accomplishment. His friends are doubtful, and demand proof. How can he prove things to them? Shall he take them to open the box in daylight? His companions will be able to see the captive, but also exert historical effects on it at the moment the box opens. Shall he take them to see the box in the dark? The creature will be immune from the doubting companions consensus, but will be invisible to it's audience. The only solution for our hunter is to get his friends good and drunk before going to see the thing, and paint it pink at the moment of capture.
This is not to say that scholars, along with variety of other bravos, opportunists, and fools, haven't continued to dash themselves against the rocks of mapmaking for the last 400 years. Not a year goes by when some young fellow claims to have found "The Spacial Clocktower". The idea of consensus direction and distance has been distracting promising technomancers for as long as the consensus has been abandoned by the rest of sensible folk.
Contemporary understanding of the phrase may refer less to the ultimate problems referred to by Alarius, and more to the problems of the modern practice of invariant metrics, that is the measurement of (geographic or other) historio-physical quantities and relations via a set of abstract consensus metrics (mis-named "Historical Invariants") and their subsequent application to concrete experience through calculation. Bindlet Ball enthusiasts are well familiar with this practice, as all games last a single ihr (invariant hour). Indeed, the games which take place in sight of clock towers are terribly dull, even if the referee calculations are a quite a bit less infuriating.
Sports fans aside, most Ghylliads, Ghyllians, and little Ghyllets are familiar with the frustration and anxiety of this approach to managing and measuring spacetime. Very few fields of endevour (excepting perhaps historical and anthropological study) are without difficulties rising from the exceptional and error prone calculations required to make even small judgements about the nature of spacetime based on abstract consensus measurements. It is for this reason that approximations like "Near", or "To the West" are so common not only in informal communications but also official literature, legal documents, and scholarly work. The large quantity of measures and directions carried forward in ceremony and social practice from the period of Kings, or inherited from various lost cultures, and the associated cost of calculation and dispute resulting from the attempt to calculate invariants and then re-apply those invariants to concrete situations, incur not only huge costs, but terrible annoyance (outside of the sporting world).
Scholars wishing to learm more about modern invariant metrics in Historio-Physics may wish to consult "Doc" Rockett's excellent introductory text on the subject, Invariant Transforms, with Historio-Physical Applications. I personally have also made extensive use of Mother Mutton's Golden Book of Linear and Dynamic Historical Projection Techniques and Coloring Fun in the preparation of the entry.