Creating Backgrounds

Background images should be a png or jpeg with recommended dimensions 1024 x 512 or 1024 x 1024 or greater (will be scaled to fit the screen).
Background images must have the appropriate map projection, center, and aspect ratio to align correctly.

World Map	Aspect	Projection	Center	proj4
Basic	`2:1`	Equidistant Rectangular	`[0,0]`	`+proj=eqc +lat_ts=0 +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +a=6371007 +b=6371007 +units=m +no_defs`
Polar [north]	`1:1`	Equidistant Azimuthal	`[90,0]`	`+proj=aeqd +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs`
Polar [south]	`1:1`	Equidistant Azimuthal	`[-90,0]`	`+proj=aeqd +lat_0=-90 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs`
Azimuthal Equidistant	`1:1`	Equidistant Azimuthal	`[LAT,LON]`	`+proj=aeqd +lat_0=LAT +lon_0=LON +x_0=0 +y_0=0 +a=6371000 +b=6371000 +units=m +no_defs` where `LAT` and `LON` define the center of the projection.
Mercator	`1:1`	Web Mercator	`[0,0]`	`+proj=merc +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +R=6378137 +units=m +no_defs`
Mercator equal-area	`1:1`	Sinusoidal	`[0,0]`	`+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs`
Van der Grinten	`1:1`	Van der Grinten	`[0,0]`	`+proj=vandg +lon_0=0 +x_0=0 +y_0=0 +R_A +a=6371000 +b=6371000 +units=m +no_defs`

The default maps use vector data from Natural Earth, and raster data from Blue Marble: Next Generation.
The default maps use a white foreground (landmasses), and transparent background (ocean). The final coloring is determined by the app’s theme.
The graticule and other markings are drawn behind the background image (requires transparency).