Total magnetic intensity reduced to the pole (TMI RTP) image overlain on tilt-filtered (Tilt) total magnetic intensity reduced to the pole image. The image is a partially-transparent pseudocolour layer of TMI RTP, with a histogram-equalised colour-stretch, overlain on a greyscale intensity layer of the Tilt, with a histogram-equalised stretch. Cooler colours indicate lower values and warmer colours represent higher TMI RTP values. Dark tones indicate lower values and lighter tones represent higher values of the Tilt. Reduction to the pole filters magnetic anomalies to appear as if the Earth's magnetic field were locally vertical, as at the magnetic pole (assuming all magnetic sources are inductively magnetised). The tilt-angle filter produces a positive maximum over the centre of a magnetic source and is zero near the edge of the source, and is useful for tracing geological structure below variable depths of cover. Variations in the magnetic field are caused by lithological factors, principally magnetite (and/or pyrrhotite) content. This Statewide image was generated by merging many individual airborne magnetic surveys.