As already noted, a number of countries define sub-national entities or administrative divisions as constituencies. Especially when they are defined in the Constitution, this is a strong safeguard against gerrymandering. That is why the Code of Good Practice in Electoral Matters encourages proceeding to reallocation rather than redistricting, at least every ten years, preferably outside election periods, and states that constituency boundaries should, where possible, coincide with administrative boundaries, by taking where appropriate into account other geographical or historical criteria.