![]() WGS 84 is widely used and supported by most (if not all) spatial databases and systems, which makes it the only choice in some situations and a safe choice in many other situations. WGS 84 is the only supported coordinate system for GeoJSON. Some spatial databases only support WGS 84 as a coordinate reference system.Data will be used with other global datasets.World Geodetic System 1984 (WGS 84) Use when: Data extents are greater than mainland New Zealand.New Zealand Geodetic Datum 2000 (NZGD 2000) Use when: Lets look at the factors to think about when choosing a particular coordinate system to use. Hopefully you’ve now decided between geographic and geometric. However, if you’re going to use the data for visualisations or analysis, and accuracy over large regions is not critical, choose a geometric coordinate system. So in general terms if you’re primarily just storing the data, or the data covers a large extent that’s greater than mainland New Zealand then choose a geographic coordinate system. Good if data is primarily being used for visualisation.Likely won’t need conversion to a projected coordinate system for visualisation.Need to consider projection or accuracy limits across large regions.Database functions will be relatively faster.Will need conversion to a projected coordinate system for visualisation. ![]() No need to consider projection or accuracy limits across large regions.Spatial database functions will be relatively slower.Stores data in longitude/latitude coordinates.There are some general pros and cons for geographic and geometric coordinate systems that will help you choose between them: Geographic (NZGD 2000 and WGS 84) In New Zealand, there are three main vertical datums that are commonly used: the New Zealand Vertical Datum 2016 (NZVD2016), local mean sea level datums (LVD) and NZGD 2000 ellipsoidal heights.Ī good approach is to first decide if it’s a geographic or geometric coordinate system that best suits your situation. Vertical coordinate systems record heights measured above (or below) a reference surface (datum). Web Mercator is used worldwide and the de facto coordinate system for web mapping applications such as Google Maps, Mapbox, and Bing Maps. NZTM 2000 is the official projection for New Zealand topographic mapping. The two projections commonly used in New Zealand are New Zealand Transverse Mercator 2000 (NZTM 2000) and Web Mercator. Different projections can preserve direction, shape, area, distance and shortest route, however, no projection can preserve all of these.Īn additional benefit of projections is that they have units of metres, which lets users measure meaningful distances directly from a map. Projections are chosen to maintain certain characteristics and to minimise the impact of the distortion. This can be visualised using the peel of an orange: it is not possible to lay the entire peel flat without breaking it in some way.Ī projection is used to manage these distortions in a predictable way. It is not possible to represent geographic coordinates on a flat surface without introducing some sort of distortion. Projected systems are a type of cartesian system that maps the earth on a flat surface with coordinates recorded as x/y values as shown in the following diagram. It is important that coordinates in terms of WGS 84 have a time associated with them, especially where the best levels of accuracy are required. These are often referred to as dynamic or kinematic coordinates. This continuous ground movement means that even in the absence of earthquakes and other localised land movements, WGS 84 coordinates are constantly changing. In New Zealand this movement is about 5cm per year. This is because the tectonic plates on which New Zealand sits are constantly moving, albeit reasonably slowly. WGS 84 by contrast is a global datum which means that coordinates change over time for local objects which are fixed in the ground. They are often regarded as the same, but NZGD 2000 provides sub-metre accuracy by accounting for the local deformation in New Zealand. In New Zealand we have the choice between the New Zealand Geodetic Datum 2000 (NZGD 2000) which is the official datum for New Zealand, or the World Geodetic System 1984 (WGS 84) which, as the name suggests, is a global geographic system.
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