Spatial reference system - clicking on the Change button will open Select Spatial Reference System window.

The CRS tab is available in Map Properties and Layer Properties (Raster and Vector layers). It has different effect depending on which item on Key pane it is set on:

Map - the CRS on Map will determine a base projection to which Earthlight will recalculate records from all layers. It should be adjusted based on the projection of Raster layers that are creating the background for the map
Raster/WMS/WMTS Layers - setting the CRS will work as a declaration and will be used by Earthlight to recalculate the extent for those layers to work with Map CRS.
Please note

Earthlight will not be able to recalculate the Coordinate Reference Systems for each tile in Raster/WMS/WMTS Layers, therefore it is imported to set the Map in such why that it match the CRS of those layers. That way the background layers define the projection for the whole map.
Vector Layers - setting the CRS will work as a declaration and will be used by Earthlight to recalculate the extent and records location from those layers to work with Map CRS.

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