Creating Backgrounds

  • The background image 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).
  • 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).
  • The background image 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.

A GIS application (e.g. QGIS) can be used to create new map backgrounds. The map data needs to be re-projected or warped (see proj4 definitions), and exported to an image with the appropriate aspect ratio. The final image should be optimized to reduce its size (e.g. pngquant).