By Henry Bell
Historian and political commentator
The boundaries of parliamentary constituencies are revised roughly every decade to ensure that the electorate of each division is broadly equal.
The present ideal number of voters for each of the 18 constituencies in Northern Ireland is around 60,000.
As Westminster elections are conducted by the first past the post system, each division returning one member only, these geographic boundaries will often give an indication of which party can win the seat.
Election battles in Northern Ireland have been dominated by a sharp divide, based on religious identification, between unionism and nationalism, since the 1880s.
In most cases, the seats created by the Boundary Commissions could easily be called for one side or the other.
This political division in Northern Ireland tends to squeeze out third parties and result in elections whose outcome could be perceived as a sectarian headcount.
In this climate, it was inevitable that some would be unhappy at the way boundaries were drawn leading to charges of gerrymandering ie boundaries that favour certain parties.
This pattern of single member constituencies, dominated by unionism or nationalism, appeared in the 1880s when Ireland was divided into 101 distinct geographical areas (there were also two University seats).
The nine counties of Ulster with 31 seats divided almost equally between protestant constituencies electing Conservatives or Liberal Unionists and Catholic constituencies electing Nationalist.
Between 1885 and 1918, there were a couple of seats that did change hand but the vast majority of seats had safe majorities; so safe in fact that many were not challenged by a candidate from across the divide.
There would be no revision of boundaries until 1918, the most remarkable change being the representation of Belfast.
The city was increased from four to nine seats, a result of the rapid growth of the urban population in the last quarter of the 19th century.
These boundaries were short lived, however, as the new Parliament of Northern Ireland was established in 1921.
The number of seats was reduced to 13 (12 divisions and one for Queen's University). This arrangement immediately provoked criticism.
Nationalists were the majority only in the two member constituency of Tyrone and Fermanagh.
In Belfast, the old divisions of North, East, South and West re-appeared but new boundaries created a unionist majority in all four. Previously nationalists had been able to take West Belfast.
Historially, there was a Queen's University seat until 1951
It would not be until 1951 that the boundaries would be again revised; the loss of the University seat left Northern Ireland's representation at 12.
Again nationalists could only win in the west of Northern Ireland, Fermanagh & South Tyrone and Mid Ulster.
Belfast was not redrawn and still sent four unionists to Westminster although there was a brief interlude in West Belfast when an Independent Labour candidate won the seat.
This remained the case until 1966 when demographic changes in the city made West Belfast a safe bet for nationalists, resulting in the election of Gerry Fitt for Republican Labour.
More sweeping changes came for the 1983 election. Northern Ireland saw its representation increased from 12 to 17 seats (18 since 1997).
Most unionists thought this revision would boost their numbers but the new constituencies included a number that had built in nationalist majorities.
Unionists did do well in 1983 winning 15 seats but this was due to vote splitting between the SDLP and Sinn Fein.
The present situation is that seven seats tend to nationalism and 11 to unionism with two or three seats that could be seen as vulnerable due to population shifts and general demographic changes.
This year, 2010, sees another alteration of the political geography of Northern Ireland, but not as wide or sweeping as previous revisions.
This is more in the nature of a tidying up process and reflects the continued population decline of the four Belfast divisions.
Six constituencies, mainly in the south and west of Northern Ireland will not be affected at all.
Outside of Belfast, the changes amount to the shuffling of a few wards from one constituency to another.
The changes in Belfast will see North Belfast take in Glengormley, from South Antrim.
East Belfast will now expand to encompass the Dundonald area.
West Belfast moves into Dunmurry and Derriaghy.
South Belfast has the most interesting change, with the inclusion of areas formally in East Belfast and also Carryduff from Strangford.
This could make it more difficult for the SDLP to hold the seat won in 2005 as this will probably increase the nominal unionist majority of the constituency.
Boundary commissions are a necessary part of the political process and they reflect the political geography of Northern Ireland.
The most striking changes over the last 50 years are the granting of new seats in the greater Belfast area and a political representation that more closely reflects the wishes of the voters.