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A provisional isogonic map of Australia and New Guinea showing predicted values for the epoch 1955.5

Created 17/10/2025

Updated 17/10/2025

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A provisional isogonic map of Australia and New Guinea has been prepared showing predicted values of declination for the middle of 1955. Along with this map, and isoporic chart is given showing the expected annual rate of change of declination over the same area for the same epoch. This rate of change (secular variation) can be taken as applying for all practical purposes from the beginning of 1953 to the end of 1957. It is expected that by the time a new map will have been prepared showing predicted values for 1960.5. The main points to note about the present map, in comparison with that for 1950.5 are: i) that the declination over Tasmania is from two-thirds to three-quarters of a degree greater (i.e. more easterly) than would have been expected from the 1950.5 map; ii) the annual rate of change of declination over the south-eastern part of Australia shows an increase in positive (i.e. easterly) value; iii) the annual rate of change of declination over the north-western part of the mainland now shows a small negative (i.e. westerly) value instead of the small positive value shown in previous years.

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Additional Info

Field Value
Title A provisional isogonic map of Australia and New Guinea showing predicted values for the epoch 1955.5
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/dataset/21177141-d535-4d2c-8275-e1460d74c3d6
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 22/04/2018
Geospatial Coverage
Map data © OpenStreetMap contributors
{
  "coordinates": [
    [
      [
        108.0,
        -44.0
      ],
      [
        169.0,
        -44.0
      ],
      [
        169.0,
        0.0
      ],
      [
        108.0,
        0.0
      ],
      [
        108.0,
        -44.0
      ]
    ]
  ],
  "type": "Polygon"
}
Data Portal Geoscience Australia

Data Source

This dataset was originally found on Geoscience Australia "A provisional isogonic map of Australia and New Guinea showing predicted values for the epoch 1955.5". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/a-provisional-isogonic-map-of-australia-and-new-guinea-showing-predicted-values-for-the-epoch-1