WDMAM World Digital Magnetic Anomaly Map


The WDMAM (World Digital Magnetic Anomaly Map) is an international scientific project under the auspices of IAGA (International Association of Geomagnetism and Aeronomy) and CGMW (Commission for the Geological Map of the World), aiming to compile and make available magnetic anomalies caused by the Earth lithosphere, on continental and oceanic areas, in a comprehensive way, all over the World. At 3 arc-minutes, the latest WDMAM version 2.1 [Choi et al., 2023] grid is now available for remote use in GMT.


You access a global WDMAM grid by specifying the special name


The following codes for rru and the optional reg are supported (dimensions are listed for pixel-registered grids; gridline-registered grids increment dimensions by one):







360 x 180


97 KB

1 arc degree global WDMAM (3 min @ 315 km)


720 x 360


352 KB

30 arc minute global WDMAM (3 min @ 157 km)


1080 x 540


763 KB

20 arc minute global WDMAM (3 min @ 105 km)


1440 x 720


1.3 MB

15 arc minute global WDMAM (3 min @ 79 km)


2160 x 1080


2.9 MB

10 arc minute global WDMAM (3 min @ 52 km)


3600 x 1800


7.7 MB

6 arc minute global WDMAM (3 min @ 32 km)


4320 x 2160


11 MB

5 arc minute global WDMAM (3 min @ 26 km)


5400 x 2700


16 MB

4 arc minute global WDMAM (3 min @ 21 km)


7200 x 3600


29 MB

3 arc minute global WDMAM (3 min original)

Note that resolutions 05m and higher are tiled. See Remote Data Sets for more information.

See GMT remote dataset usage for when resolution codes are optional or required. All of these data will, when downloaded, be placed in your ~/.gmt/server directory, with the earth_wdmam files being placed in an earth/earth_wdmam sub-directory. If you do not specify a CPT, the default CPT for this dataset (@earth_wdmam.cpt) will be used.

Technical Information

We scale and reformat the original data to take up very little space so that downloads from the servers are as fast as possible. For the WDMAM grid this means we chose 0.2 nTesla as the smallest data unit, which is well below the uncertainties in the model. Data are scaled and shifted to fit in a short integer grid that is highly compressed by netCDF lossless compression and chunking. The data are reported in nT.

Data References

  1. Choi, Y., Dyment, J., Lesur, V., Garcia Reyes, Catalan, M., Ishihara, T., Litvinova, T., Hamoudi, M., the WDMAM Task Force*, and the WDMAM Data Providers**, World Digital Magnetic Anomaly Map version 2.1, map available at https://www.wdmam.org/.

* The WDMAM Task Force: J. Dyment (chair), M. Catalan (co-chair), A. de Santis, M. Hamoudi, T. Ishihara, J. Korhonen, V. Lesur, T. Litvinova, J. Luis, B. Meyer, P. Milligan, M. Nakanishi, S. Okuma, M. Pilkington, M. Purucker, D. Ravat, E. Thébault. (alphabetical order)

** The WDMAM Evaluators: C. Gaina, J. Luis, S. Maus, B. Meyer, M. Nakanishi, M. Purucker, Y. Quesnel, R. Saltus, P. Taylor. (alphabetical order)