I wanted to decorate my apartment with a tube map just like the ones they have in stations. The posters they sell are a different design and are not available in the same sort of size. TFL doesn't routinely release the station poster design digitally either.
Fortunately, TFL supplies copies in response to FOI requests
Unfortunately, it's in the form of a lossy JPEG inside a PDF.
Fortunately, there exists an extremely good vectorizer called Vector Magic.
Unfortunately, it only supports inputs below 4 megapixels, and its batch mode isn't very configurable and can't use the same image color palette between runs.
Fortunately, computers have to do whatever we ask. So we use a user-space MachO loader and do some reverse engineering to manually use invoke its vectorizer in order to convert the whole map in chunks.