[Beta] 4G Cover Levels Zoom

Generalisation of operators’ 4G coverage layers for smoother display at different zoom levels.

Allows easier use of cover data published by Arcep for display purposes.

Starting from OSM zoom levels Zoom Levels — OSM
and after a few tests, here is the correlation simplification/zoom level (scale):

— 2.500 m: visible > 1:4M
— 1.000 m: 1:4M <= visible < 1:2M
— 500 m: 1:2M <= visible < 1:1M
— 250 m: 1:1M <= visible < 1:250k
— 100 m: 1:250k <= visible < 1:150k
— 50 m: 1:150k <= visible < 1:35k

Beyond a simplification at 2.500 m the volume of data is so low and the quality very insufficient, that it is not worth making even more drastic simplification.