Indicate quadrants that aren't rendered due to excess data

[hampelm]

There's no indication we have data there.

Two things to try would be a very transparent single color and a very transparent hazard stripes-type pattern (in our colors, of course)

[prashtx]

I assume here that "quadrant" means a tile. Otherwise, if we want to indicate that a sub-tile area has data but isn't rendered to full fidelity, we're essentially talking about rendering a "coarse tile", as in #104.

I like the idea of visually indicating that we've run into the limit of how many responses we're willing to fetch and render. Something like translucent hazard stripes sounds nice, but a single transparent overlay would be much simpler, since it could be a style applied to the entire tile rather than a set of shapes to draw.