ST_Area(geometry) with ogrinfo estimates a stable area per grid cell

Question

I use ST_area(geometry) in order to calculate the area of each grid cell of a vector grid with LCC projection and 6x6km2 resolution. The CRS of the vector is: +proj=lcc +lat_1=45 +lat_2=22 +lat_0=38.7 +lon_0=20 +x_0=0 +y_0=0 +a=6370000 +b=6370000 +units=m +no_defs

I do the following:

ogrinfo -dialect SQLite -sql "SELECT id,ST_Area(geometry) as AREA FROM grid" grid.shp
ogrinfo grid.shp -sql "ALTER TABLE grid ADD COLUMN AREA_grid float"
ogrinfo grid.shp -dialect SQLite -sql "UPDATE grid SET AREA_grid =ST_Area(geometry)"

The result is that the area_grid takes the value of 36000000m2 for all grid cells. This is not correct since the real area of grid cell slightly varies in different coordinates.

Do I have to define in a different way the area of the grid cell?

Answer 1

Your grid is 6km x 6km so each cell will remain 36 square km. No matter what your projection each grid cell will be the same. The shape of each grid cell will likely change. Whether you can perceive this in your data. I'm not sure

Answer 2

LCC is not an equal area projection, see https://en.m.wikipedia.org/wiki/Lambert_conformal_conic_projection

GDAL's ST_Area computes the area in 2D cartesian space, it does not consider the shape of Earth.

This means you get simple, "dumb" values, not the actual area in Earth meters.