Use responsive images to render a clearer map.

[adunkman]

On the Service Request page, we render a static image of a Google Map:

That image is slightly blurry in this screenshot, which is due to resizing (fixed in #7).

It’d be nice if we could check the size of the map on a few mobile devices and have Google render differently-sized maps to reduce this blur effect as much as possible (and at 1x and 2x pixel densities) using Responsive Images.