Calculating magnetic variation and annual change for compass roses (Maritime Charting)

The following steps outline how to calculate the magnetic variation and annual change to the appropriate attributes in the Nautical data model.

Ensure that you are not in an edit session.

Steps:

1. Start ArcMap.
2. On the main menu, click Customize > Toolbars > Nautical Cartography.
3. On the Nautical Cartography toolbar, click Geoprocessing > Magnetic Calculator.

   The Magnetic Calculator dialog box opens.

4. For the Input Features parameter, drag and drop TidesAndVariationsP from the Table Of Contents window or choose TidesAndVariationsP from the drop-down list.
5. For the Altitude parameters, accept the default values of zero (0) and Meters.

   Most nautical charts will have a zero Altitude, so these values are necessary but arbitrary.

6. Enter the date in the format of mm/dd/yyyy if you alter it from the current date.

   The Date parameter defaults to the current date; however, this can be changed to go as far back as 1/1/2005 and projected forward as far as 12/31/2014.

7. For the Magnetic Component Field(s) parameter, choose DECLINATION from the drop-down list if using S-57 data.
8. Choose VALMAG from the Field column next to DECLINATION if using S-57 data.
9. For the Magnetic Component Field(s) parameter, choose ANNUAL_DRIFT from the drop-down list if using S-57 data.
10. Choose VALACM from the Field column next to ANNUAL_DRIFT if using S-57 data.
    If using S-57 data your results will be similar to the following:

    Note:

    If using non-S-57 data, identify which fields will be calculated, or simply enter the name as a new field.

11. Click OK.