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Coordinate reference system
Plain-language definition and practical context for Coordinate reference system.
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Definition
A coordinate reference system (CRS) defines how coordinate values relate to positions on Earth, including the datum, coordinate system, units and often axes. Check each layer’s CRS metadata before combining it; changing a CRS label is not the same as transforming coordinates.
How to apply this
New Zealand example: LINZ describes NZGD2000 as the official geodetic datum and NZTM2000 as a projected system based on it. LINZ lists NZTM2000 as EPSG:2193 for 2D mapping of mainland New Zealand when metric units are needed. Check the layer’s own metadata before using or transforming it; do not infer a CRS from coordinate values alone.