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Ocentric vs Ographic latitudes

Ocentric vs Ographic Latitude

Latitude can be defined in two common ways: ocentric and ographic. Ocentric latitude is measured from the equatorial plane using a line drawn from the center of the body to the surface point (center-of-body latitude). Ographic latitude is measured from the equatorial plane using the surface normal (a line perpendicular to the body’s reference shape at that point). On a body represented by an ellipsoid (or other non-spherical reference shape) they differ, with the maximum difference occurring near mid-latitudes (around 45°).


1) The two latitude types

Ocentric latitude

Also called: planetocentric (planets), geocentric (Earth)

  • Uses a line from the planet’s center to the surface point.
  • Think: “angle from the equator as seen from the center.”

Ographic latitude

Also called: planetographic (planets), geodetic (Earth), and often “geographic latitude”

  • Uses the surface normal (perpendicular to the body’s reference shape) at that point.
  • Think: “latitude based on the reference surface.”

Note about “geographic”: The word “geographic” is used loosely in many GIS contexts to mean “lat/long,” and that latitude is typically geodetic—which corresponds to ographic.


2) Reference shape matters

The quickest way to think about this is by the shape your data assumes:

  • If your data is tied to an ellipsoid (flattened sphere) reference shape, it is almost always using ographic latitude (surface-normal / geodetic-style latitude).
  • If your data is tied to a sphere reference shape, it is often using ocentric latitude (center-of-body latitude).

On a perfect sphere the two definitions produce the same numeric latitude values; the difference shows up when the reference shape is not spherical.


3) Common confusion

This is only about the definition of latitude. It is not the same as:

  • choosing whether longitude is positive east or positive west
  • choosing whether longitude is 0–360 or −180–180
  • choosing a map projection (equirectangular, polar stereographic, etc.)

Those are separate settings. You can have the right longitude/projection and still be wrong on ocentric vs ographic (and vice versa).


4) Which option should I pick? (simple guidance)

If you are working with Earth

Earth data can be referenced to a sphere or an ellipsoid, but most Earth GIS data uses an ellipsoid, which corresponds to ographic latitude.

Most likely correct on Earth: ographic

If you are working with a planetary body other than Earth

Non-Earth datasets vary, but many modern planetary products are commonly distributed in ocentric (planetocentric) coordinates.

Most likely correct for non-Earth planetary data: ocentric

If your dataset explicitly says planetographic (or uses a defined ellipsoid and states geodetic/planetodetic), then choose ographic.

Best rule (when the metadata is clear)

  • If the dataset says planetocentric / geocentric → choose ocentric
  • If the dataset says planetographic / geodetic → choose ographic

5) Quick validation checklist

  • Check a few known features (craters, dataset seams, landmark points).
  • If the map is consistently shifted north/south (but longitude looks right), you likely picked the wrong latitude type. Switching ocentric ↔ ographic often fixes a clean north/south offset.
  • If the map looks mirrored or shifted east/west, that is more likely a longitude convention or projection issue, not ocentric/ographic.

One-sentence summary

Ocentric = planetocentric = geocentric (center-of-body latitude)
Ographic = planetographic = geodetic (surface-normal latitude; often what people mean by “geographic latitude”)


For more information:

Image one is from Encyclopaedia Britannica, Inc, https://www.britannica.com/science/latitude

Image two is from Proj, https://proj.org/operations/conversions/geoc.html