A multi-national project to upgrade the mapping of magnetic anomalies has resulted in a report, map, and data. The U.S., along with Canada and Mexico, cooperated in this project which brought together data from a variety of survey projects.
Magnetic anomaly refers to the variation in the strength of the magnetic field, and is used by geologists to infer structure and materials of the earth’s crust that are too deep to be sampled easily.
The magnetic field can be measured by airborne instruments. Data collected over Wisconsin is in the highest-resolution category, flight lines being spaced no more than 1 kilometer apart.
To view the map (in PDF format), read the report (PDF or text), or download the gridded data, consult the project web site.
More information: North American Magnetic Anomaly Project