The "true" centroid is the centre of mass of that polygon, such that if some flat substance of uniform thickness and density were cut into the shape of that polygon, then that object would balance at the centroid. The centroid is a useful way of summarizing the location of a set of polygons as points, particularly when used for comparative analysis. Note that the centroid could potentially fall outside the SA2 polygon, depending on the shape of the polygon.The dataset contains the EASTING and NORTHING attributes of the centroid point in NZGD2000 New Zealand Transverse Mercator (EPSG:2193) and LATITUDE and LONGITUDE of the centroid point in decimal degrees in WGS1984 (EPSG:4326) projection.
SA1s are based on the meshblock pattern. Non-alignment of meshblock to cadastral boundaries is one of a number of reasons for meshblock boundary adjustments. Other reasons include requests from local authorities, Local Government Commission, Electoral Representation Commission, and to make census enumeration processes easier. From the meshblock pattern, higher geographies, including the 2021 SA1 pattern, were dissolved using the dissolve tool in the Arc GIS suite. To derive the SA1 boundaries clipped to the coastline, meshblock polygons were dissolved to exclude meshblocks with a land/water attribute of Inlet or Oceanic.
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