Geometry Postgis 4326 vs Geography

Question

after browsing the webpage and postgis in the action book. I still don't get 4326 geometry and geography.

As I understand it, geometry is the projection of the map onto the surface, and geography is a three-dimensional representation (model WGS86).

If both of them are equal 4326, what are the benefits of using one over the other and what will be such cases.

I know that geometry has more functions, and they claim that these functions can be much faster than geography, but then what is used for the geographic model if you can use 4326 geometry?

Edit: When I talk about geometry, I mean only 4326, not others.

Answer 1

The documentation should answer most of your questions and even has a FAQ section on that particular topic. The choice of which type to use really depends on what you do with your data.

But to clarify some of the misunderstandings in your question: no, geography is not necessarily a three-dimensional representation. Both types support 2D and 3D geometric representations.

Answer 2

There is a big difference. Geography is much more accurate, but much more resource intensive. Geometry will, for example, produce distances in units of SRID (in degrees) that are not significant to you. Geometry treats lines as lines n on the projected surface, while in reality the lines from point A to point B are arcs of large circles (this means that the geometry will return incorrect results for intersections, etc.).

In short, geometry uses plane geometry and geodetic calculations on an ellipsoid.