The Selwyn District lies in central Canterbury, and occupies a central position in the South Island.
Boundaries: On the Canterbury Plains, the Waimakariri River forms the northern boundary; in the hill country the border with the Hurunui District is more arbitrary. The eastern boundary comprises (from north to south) the city of Christchurch, Banks Peninsula, and the South Pacific Ocean. The southern boundary is the Rakaia River, beyond which lies Ashburton District. The western boundary is the main divide of the Southern Alps.
Geographical features: Selwyn District contains within it two distinct regions: the plains and the high country. The plains, where most of the population lives and the majority of activity takes place, form an expanse of low-lying, flat, and comparatively dry grassland. The extreme south-east is dominated by Lake Ellesmere (Te Waihora), an expanse of water surrounded by marshes, formed by the out-flow of the Selwyn River. The tributaries of the Selwyn River include the Waianiwaniwa River, the Hororata River and the Hawkins River.
The high country is a sparsely-populated region, mainly consisting of hill and mountain ranges and narrow river valleys. Most of the high country is grassland, including some tussocklands; areas of beech forest remain within the Craigieburn Forest Park and the Arthur's Pass National Park.
Population: The total population of Selwyn District was 44,595 in the 2013 Census. 2013 Census information confirmed that Selwyn District is the fastest growing area of New Zealand. Selwyn’s population grew from 33,642 to 44,595 between 2006 and 2013, a 33% increase. The average growth for New Zealand as a whole during that period was 5.3%.
Approximately half the population lives in the various towns and villages in the district, while the remainder are on farms. 95% of the population live on the plains. The largest towns are Darfield, Leeston, Lincoln, Prebbleton, Templeton and Rolleston which is also the home of the Council's main office. The towns of Springfield and Sheffield are on State Highway 73, where the foothills start to rise from the Canterbury Plains.
Climate: The plains have a temperate climate, characterised by warm, dry summers and cool winters. The Southern Alps are responsible for the relatively low rainfall, and also lead to a foehn wind, the "Canterbury Nor'Wester". This strong, hot and dry wind is most common in spring and summer, and on occasion reaches damage-causing strength. In the mountain country of the Southern Alps, conditions are much colder and wetter.