This is already mentioned in the other comments, as the latitudinal correction to longitudinal dimension [i.e. use cos(latitude) as a scale for EW distances].
I call this the tangent-plane projection (which hints at your picture), where distances can be simply calculated by 2D Pythagoras in the EW-scaled coordinates. I recently discovered it is more often known as Equirectangular Projection:
I call this the tangent-plane projection (which hints at your picture), where distances can be simply calculated by 2D Pythagoras in the EW-scaled coordinates. I recently discovered it is more often known as Equirectangular Projection:
https://en.wikipedia.org/wiki/Equirectangular_projection
More details at this excellent resource for GIS coordinate geometry:
https://www.movable-type.co.uk/scripts/latlong.html