A short guide to QGIS 3 Coordinate Reference Systems (CRS)

In this tutorial we will discover how to use QGIS 3 coordinate reference systems: their usage in the projects, how to set a layer projection, how to change the geographic projection of a layer, both temporary and permanently.
COORDINATE REFERENCE SYSTEM❓
A spatial reference system (SRS) or coordinate reference system (CRS) is a framework used to precisely measure locations on the surface of the Earth as coordinates. It is thus the application of the abstract mathematics of coordinate systems and analytic geometry to geographic space.
🌍 What is QGIS?
QGIS is a professional GIS application that is built on top of and proud to be itself Free and Open Source Software (FOSS).
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[@loggingman72]

Great , thank you for your effort and time to explain in a good way.

[@hsahil_10]

Thank you for the nice explanation.

[@rajanhumagai]

Which system we have to choose for Australia ?

[@talesfromthegis]

Take a look to epsg.io/?q=australia and choose the one that fits better for your case :)