Because of SOS’s high resolution requirements, it is generally easier to have a
base map of vector data, which can be scaled indefinitely. Raster, or image,
data works if it is high enough resolution, but images of sufficiently high
resolution are uncommon.
Additionally, SOS’s software needs to be given a specific map projection in
order to render the map correctly on the sphere. In QGIS, this is the default
projection: the Equatorial Cylindrical Equidistant projection, also known as
WGS 84 or EPSG:4326. While this is a relatively common map projection, it is
NOT the one used by anything that Google Maps has made, or anything with Google
Maps as a background. There are a lot of tutorials for QGIS that assume a
Google Map will be a fine base map, so they tell users how to import that and
skip over the instructions for importing anything else.
Because of this limitation, the underlying map layer is a little more
complicated when making an SOS map than it is when making a normal map.
It is certainly possible to import a vector map in the correct projection.
They’re just not very easy to find. A good place to go is Natural Earth
Data. Click on the green Get the
Data button near the top of the page. From that page, you can
download the “Natural Earth quick start kit” or browse the available resources.
If you choose to download the quick start kit, you will get a zip file that
contains a folder called “packages”. Inside is a .qgs file called
“Natural_Earth_quick_start_for_QGIS.” To get started, it’s a fun one to play
It is also possible to put an image as the base of your map, provided the image
is of high enough resolution (2048×1024 or 4096×2048 pixels for SOS). SOS’s FTP
server is a good place to find high resolution
images that are already in the right format.