The majority of recordings on the general sound map are simply of curious or distinctive sounds heard around London. Some also appear elsewhere as part of the 12 Tones of London statistical recording project, and here are subsumed into their appropriate grid squares.
These kinds of recordings always have descriptive file names which don't require any further explanation. But just over a hundred others have ones consisting only of the letters 'TQ' followed by eight digits. These are the Ordnance Survey co-ordinates marking the exact centre of each of the sound map's 112 grid squares, and so these file names tell you with some precision where the recordings were made. Reaching each point was done with the help of a GPS receiver and a willingness to scramble over fences and run onto golf courses. The contents of those recordings are summarised in the graphic below:
The key on the left-hand side shows the most common sound categories encountered. The louder a particular sound type encountered at the centre of a grid square, the darker its icon. More than one icon of the same kind means that sound takes up more of the recording's length. Despite the wide spacing of the recording points and the brief duration of the sound files, they seem to do a reasonable job of plotting in outline the common or persistent sound types heard around London during the daytime.