The electoral system describes a crucial set of rules which details how the votes are cast and used.  Given the importance of legitimacy for the parliament and government elected by it, it is vital that the system chosen reflects widely held values about elections and what determines a winner.

In every electoral system there are three core elements:

• how voters express a preference
• the unit in which voters are organised and votes counted, called electorates in New Zealand
• how the winner or winners are determined.

The MMP (Mixed Member Proportional) system used in New Zealand gives each voter two votes, an electorate and a party vote.  Electorate votes are counted in each electorate on the basis of First Past the Post (FPP or plurality).  Party votes are counted across the entire country using a proportional representation formula (Sainte Lague).

The FPP system that was used in New Zealand prior to 1996 gave each voter one vote, organised voters into electorates, and used plurality rules to find the winner in each electorate.

The STV (Single Transferable Vote) system used to elect district health boards and some councils asks voters to mark candidates in order of preference.  STV uses electorates in some cases, but in other cases counts all votes together and uses the Hare formula.

How voters express a preference

The ways in which the choices are presented to voters, and how voters can indicate their views, vary greatly between systems.  Voters may be given a choice between candidates or between parties, or both.  In a referendum voters may be choosing between policy options.

Faced with a list of alternatives, a voter can indicate their view in one of two ways: they can either place the candidates (or options) in order of preference or indicate the one(s) they like.  The simplest and most common method of indicating who they like is to vote for one candidate, using a tick or a cross.  In some situations requiring the election of more than one person the voter may be able to place as many ticks as there are positions to be filled.  In such a case the voter does not indicate whether they like a particular candidate or candidates more than others.

Preference voting, on the other hand, allows the voter to put candidates or options in order, but not to indicate that they like two candidates equally, or like their third preference a lot more than their fourth.  Some systems insist that all candidates are given a preference ranking while others allow a voter to stop numbering at any point.

Decisions on which method to use relate to ease of voting, ease of counting, the kind of options available, history, norms and traditions, and the experiences of other countries.  Making the act of voting easy for all voters is an important component of ensuring equitable participation.  In countries where there are low levels of numeracy, or where people are unfamiliar with numerals, it would be problematic to have a system that requires voters to number the options.

How voters are organised - electorates

Elections are held in order to identify the representative chosen by the voters.  A common idea is that each representative will represent a particular group of voters.  In New Zealand the norm has been for this to occur by having one MP for each electorate.  This method is common in the Westminster democracies (those derived from the UK parliament) but uncommon in continental European countries.  In many democracies multiple representatives are elected by voters in a large area, or the whole country.  For instance, in the Netherlands all MPs are elected by voters across the entire country, while in Sweden voters in each city or region elect a number of representatives.

Where the country is divided into electorates, electorate boundaries have to be determined.  A number of factors are taken into consideration when drawing boundaries and countries vary on which factors they emphasise, how often they review boundaries and who does the review.

Because electorate boundaries can impact on election results (particularly those using FPP) most countries give the job of establishing those boundaries to an independent body.  When politicians or political parties are involved, there may be the temptation to draw boundaries that help or hinder a particular party.  When boundaries are drawn in this way it is known as a gerrymander.  The term comes from a cartoon in the USA in which a politician called Mr Gerry proposed boundaries that created a long, curved electorate that the cartoonist portrayed on the map in the shape of a salamander, calling the electorate a gerrymander.  Now the term is used to describe any situation in which boundaries are drawn primarily to help or hinder a particular party or candidate.

Common factors that are considered in deciding on electorate boundaries are:

• equal population size
• community of interest
• compactness
• geographic or communications features.

Equal population size

The underlying aim is to ensure that each vote has the same value. Clearly, if one electorate had 10 people and another had 100 people, any voter in the smaller electorate would have a greater chance of influencing the result.

There are a number of inherent problems in attempting to ensure equal numbers of voters across electorates.  As people often move, the number of voters in each electorate changes every day so electorate populations can never be exactly equal.  For this reason, each system specifies a variation margin: 5% in New Zealand, 1% in USA, 10% in Australia.  In Canada there are vast differences in electorate populations in recognition that in some regions people are dispersed across a large geographic area.  Where the aim is to give electorates equally sized populations, the geographic size of electorates can vary vastly.  In New Zealand, compare the geographic size of any city electorate to the West Coast electorate, or Tamaki Makaurau to Te Tai Tonga.

A related issue is how many people to have represented by an electorate MP.  Democracies vary vastly in the number of people represented per MP.  In New Zealand the target electoral population in 2007 was 57,500.

In countries with multi-member electorates, rather than change electorate boundaries in response to shifts in population, changes may be made to the number of people elected from an area.  In some Pacific nations, where an island might be an electorate, extra MPs have been added in areas with growing population to maintain some equity among electoral populations.

Community of interest

As the representative is meant to be representing a group, one would expect the electorate to contain people with similar concerns, needs or viewpoints.  A community can mean those who live in one area, such as a village or suburb, or it can mean a group of people who possess a strong collective identity.  So in order to respect a community of interest, a boundary might keep all of a town in one electorate or keep farming areas together, or it might be drawn along an iwi boundary to avoid dividing the iwi.

The idea of boundaries that encompass a community of interest only works when the community of interest is geographically defined.  When people who have a strong collective identity do not live in the same area, it is very hard to take this into account when drawing boundaries.  In the USA there have been arguments that boundaries should be drawn so that African-Americans (or Hispanics or Native Americans) living in the same town are in the same electorate.  The resulting electorates are often odd shapes, for instance taking in a series of housing areas along a major road.  The drawing of such electorates in the USA is controversial and the boundaries are often argued over in court.  Proponents call them minority-majority districts and opponents often call them ethnic gerrymanders.

New Zealand uses another approach to community-of-interest electorates in having Māori electorates.  The whole country is divided into general electorates and also Māori electorates, so that any physical place in New Zealand is in two electorates.  The idea is that Māori can choose to be part of a Māori community of interest.  Every enrolled Māori can choose to be on the Māori roll or the general roll.  No other developed democracy uses a similar system.

Compactness

In order for the representative to be able to move around the electorate and to meet with voters, the ideal is for a compact electorate rather than a long thin one.  Related to this is the idea that no part of the electorate should be geographically isolated.  Also, any odd shape could lead people to suspect a gerrymander.

Geographic or communications features

These factors relate to ease of organisation during an election, how easy it is for the representative to move around, and may relate to community of interest.  For instance, it usually makes sense to use a mountain range as a boundary because there will be little travel across the mountains.  However, a river may divide communities because there are few bridges or, conversely, unite the communities who use it.  In New Zealand, communication lines were a strong factor in moving the Chatham Islands from a Christchurch electorate (where the boat went) to Rongotai in Wellington (where the planes fly).