Chandler, Val W.Total magnetic intensity anomaly, contour, scale 1:250,000. Interpretation of magnetic data collected from airborne surveys, the map contours (lines of equal magnetic intensity) indicate the distribution and concentration of magnetic minerals (primarily iron-bearing) within the upper crust of the earth.PDFengMinnesota Geological SurveyPublicAeromagnetic map of Minnesota, St Louis county, Plate 2MapsMinnesota1983University of Minnesota