Auto detect when viewport is really far from any data

[kaligrafy]

Example: you move the viewport to the middle of the ocean (by error, or you just forgot you did so), then you are wondering why the map is blank (it happened right now to @greenscientist)

Claude.ai provides some good ideas to deal with that:

Ah, that explains it! When your map center was set to the middle of the Atlantic Ocean, you were essentially looking at an area with no detailed aerial imagery, so you got the black background (which is often the default base color for areas without imagery or data).
This is actually a fairly common issue with map applications. The Atlantic Ocean has limited aerial imagery compared to land areas, and depending on your zoom level, you might just see the base ocean color - which in many map styles defaults to black or very dark blue.
Some solutions going forward:

• Add validation to ensure your initial map coordinates are within areas with good coverage
• Set default fallback coordinates if the user somehow navigates to a low-data area
• Consider adding a simple ocean/water style that's more visually informative than black
• Implement bounds limiting to prevent users from navigating too far into oceanic regions

Good detective work finding the issue! Sometimes the simplest explanations are the correct ones. Map centering issues can be particularly tricky to spot when everything else seems to be working correctly.

[kaligrafy]

Related to #76