realwallpaper, a live world map centred on a location

  /?location=LAT,LON&variant=VARIANT&overlay=OVERLAY&size=WxH

  location  degrees, south/west negative, rounded to 0.01 (default Berlin)
  variant   lens (zoomed in on location), plain (no distortion),
            mercator (classic north-up map)        (default lens)
  overlay   none, sky (sun, moon, planets), krebs (sky and krebs nodes),
            stars (all of that plus constellations) (default sky)
  size      up to 3840x2160                          (default 3840x2160)

Renders are cached for 10 minutes. Ones that get picked up are kept
fresh in the background, so after the first request they come instantly.