The risk of inequalities of representation (electoral geometry) is particularly high in systems with one-member constituencies. Clear rules should be adopted to ensure a “clear and balanced distribution of seats among constituencies on the basis of one of the following criteria: population, number of resident nationals (including minors), number of registered voters, and possibly the number of people actually voting. The permissible departure from the norm should not be more than 10 % and should certainly not exceed 15 % except in special circumstances (protection a concentrated entity, sparsely populated administrative entity) the distribution of seats must be reviewed at least every ten years, preferably outside election periods.”34 The choice of the criterion for allocating seats (such as population or number of registered voters) should be based on the data which are most reliable.