From ErfWiki

Proposed Canon

One of the three axes of magic (along with Fate and Numbers) used to break a major class of magic into its different disciplines.

Class\Axis	Erf
Hocus Pocus	Findamancy
Spookism	Turnamancy
Stuffamancy	Dirtamancy
Eyemancy	Lookamancy
Hippiemancy	Flower Power
Naughtymancy	Shockmancy
Stagemancy	Hat Magic
Clevermancy	Luckamancy

Speculation

Erf, possibly derived from the word "Earth", tends to deals with places and things within the terrain - specifically a given hex. Thus, Lookamancy allows you to peer into a given hex while Findamancy might indicate the hex a target is located in. Dirtamancy can physically manipulate a hex's terrain value, as Sizemore did in page 126 when he opened a tunnel under his adversaries. Shockmancy, on the same page, appears to damage all units in a given hex. And, of course, the grand Spell effect on page 135 allowed Sizemore to remake a large number of hexes all at once.