The overhauled census in mainland France and the overseas départements (DOMs) introduced different methods for collecting data and for the annual calculation of legal populations according to whether municipalities were above or below the 10,000 inhabitant threshold. Because of the significance of this threshold in the census process, municipalities where the population moved above or below it were monitored particularly closely. Decree no. 2003-485 of 5 June 2003 sets the time limit for taking threshold-crossing into account in legal populations: when a municipal population has crossed this threshold upwards (or downwards) on two consecutive occasions, INSEE has three years (or five years) to change the data collection method in the municipality so that it corresponds to the new status. This period of time is needed to adapt the collection method: preparation of exhaustive collection for municipalities that now have fewer than 10,000 inhabitants and constitution of a sampling frame (Address Control List or ACL) for those that now have 10,000 or more. Since 2009 (second publication of legal populations based on the overhauled census and hence potentially the second crossing of the 10,000 inhabitant threshold), about fifty municipalities have been involved in a change of collection method; every year there is a new wave of municipalities whose census data collection method must be adjusted. Particular care must be taken when compiling an ACL for the new municipalities of 10,000 inhabitants or more because the quality of the census results for these municipalities depends on it, via the quality of the samples drawn from it. Crossing the threshold also requires introducing transitional methods for calculating legal populations and statistical results from the renovated census, both for municipalities moving above this 10,000 inhabitant threshold and for those moving below it.