The Yellow Badge Knowledge is the knowledge you need to undertake if you wish to ply for hire within 1 of 9 specific sectors around the edge of the Greater London Authority area. These 9 sectors consist of 22 London Boroughs and some sectors cover more than 1 Borough, the largest consisting of 4 Boroughs, see map below.
You need to learn between 30 and 51 runs depending on the sector you choose together with 1/2 mile areas at the beginning and end of each run. You will only be allowed to ply for hire within that sector, although you are obliged to take customers up to 12 miles on any one journey. If this journey takes you outside your sector you must return to your sector before you can legally ply for hire again. Having qualified in one sector you can then commence learning another sector if you wish. However you are only allowed to learn one sector at a time.