Sound map recordings fall into two kinds, shown by the filenames they're given.
A sound grid recording has a filename beginning with the letters 'TQ', followed by eight digits. These are the Ordnance Survey co-ordinates for where the recording ought to be made. Each is part of a regularly-spaced series of recordings covering London. More about them, including graphics showing the resulting city-wide patterns of sounds, can be found on this page.
Other recordings have more descriptive filenames and these are simply of curious or distinctive sounds heard in different places.