The 'Physical' layer which can be selected in the 'background' layers such as Google Maps, Satellite/Aerial imagery and Terrain layers has been created as a composite imagery got from several sources of data :
Contrary to nautical maps which are pre-processed and directly accessible on our servers, the raster tiles from this Physical layer are created on-the-fly by our map contour rendering engine in our servers.
This explains the display is much longer than for nautical layers.
More users will play with this layer in all regions of the world and for different levels of scales, more tiles will be created on our server, so available for all.
In the same time, the cache memory of the web browser will help to refresh faster when the user will display the same area.