Data was collected in two ways: a two-week information gathering exercise (usually undertaken during a period in October), followed by a one-night snapshot count in November.
Casglwyd data mewn dwy ffordd: ymarfer casglu gwybodaeth am bythefnos (a wneir fel arfer yn ystod cyfnod ym mis Hydref), ac yna cyfrif o un noson ym mis Tachwedd.