Units to dimensionalise area in pygplates

Q&A
1

Hi all,

I am writing to check that the squared radius of Earth in kilometres (km), as opposed to the squared radius of Earth in metres (m) should be used to dimensionalise areas returned by the pygplates get_area function?

I am asking because the documentation suggests that kilometres should be used, although the unit of length in the international system of units (SI) is the metre.

Thank you in advance for your help!

Cheers,

Nico

2

Hi Nico,

The units are in kms only because most references to Earth radius seem to be in kms. You’re right that it probably makes sense to use metres, but I guess it’s a bit like using My instead of years.

And, in case anyone else is wondering, the area of a polygon is dimensionless in that it’s the area on a unit sphere (radius of 1.0). So the area of the entire sphere is 4*PI.

Then you can choose which Earth radius you prefer:

pygplates.Earth.equatorial_radius_in_kms: radius at equator (6378.137 kms)
pygplates.Earth.polar_radius_in_kms: radius at the poles (6356.7523142 kms)
pygplates.Earth.mean_radius_in_kms: mean radius (6371.009 kms)

…and multiply your unit-sphere area by that radius squared.

Regards,
John

3

Thank you for the information, John :slight_smile:

Nico