If the geomagnetic anomalies are caused by magnetic iron deposits within granitic intrusions, then an association between most AOP activity on the map and granitic intrusions is implied.  Why would there be such an association?  There are several possible reasons: 1)  AOP lights are really Earth lights, and there is some unusual and as yet unexplained phenomenon occurring between the atmosphere and iron-rich deposits in the ground. 2)  If the AOP represent intelligently controlled craft using an unknown or poorly understood source of energy, the use of iron-bearing (mildly magnetic) granitic intrusions for underground dwellings might be due to structurally- and electromagnetically- desired qualities of that rock as wall material for underground chambers.  One could argue that surrounding fissile black shales of the Ordovician Snake Hill Formation make notoriously poor wall material due to their poor tensile strength in planes of cleavage.   Therefore, the preferred type of rock in the valley for excavation would be the granitic masses. 3)  Entrances to underground dwellings are intentionally located where geomagnetic anomalies occur at the surface as a means of camouflage. If the brightening of a plasma envelope around an AOP has something to do with opening a portal to an underground chamber, there may be residual effects that can be detected magnetically.  The association of entrances with natural geomagnetic patterns could be for both physical and psychological camouflage, given the propensity of humans to accept "rational" or acceptable explanations over an explanation which would challenge dogma and beliefs.