The task is to calculate areas for small project sites (polygons) in various Chinese cities. The dataset is available as EPSG:4490, the project CRS is also set to EPSG:4490. To get accurate comparable areas I should use an equal area projection for China, such as Asia North Albers Equal Area Conic (ESRI:102025)
To calculate the areas there are 2 options in QGIS (3.16.11):
- Create a new field with the field calculator
area(transform($geometry, 'EPSG:4490','ESRI:102025')). I got it from a different question in this forum. Used functions: area & transform
- add Geometry attributes calculated by layer CRS after reprojecting from EPSG:4490 to ESRI:102025 (including
My problem with 1. is that it returns the area not in m². From my knowledge as the unit of ESRI:102025 is specified in meters, it should use that. I don't find any other unit in the settings, which should override that. If I use 2. it gives me m².
Of course I could add the area I get from 2., back to the source (EPSG:4490), or just stick with ESRI:102025 for the data, but I'm eager to learn more.