What is the difference between UTM and WGS in a GIS software? What is the significance of both in specifying locations on the earth?
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Difference between UTM & WGS in GIS software:
UTM and WGS both are examples of coordinate systems.
These are two different but related concepts.
WGS (these days usually WGS84, but there were also WGS72, WGS66, and WGS60, and WGS84 is currently on its 5th revision/update) is a datum and ellipsoid that model the Earth. The ellipsoid used is its own, but it is so close to the GRS80 ellipsoid that it makes no practical difference. The datum provides the following information:
That’s basically what a datum is (and does), and all datums have to do this. WGS84 does a bit more than that, but it sets the foundation for a global reference frame that links everything.
As an aside, it’s also the reference frame used for GPS, and it is directly connected to the various ITRF (International Terrestrial Reference Frame) instantiations.
UTM is a map projection system: Universal Transverse Mercator. A map projection allows you to take any latitude/longitude based location on the Earth and transform it into an E/N (or X/Y) location on a plane cartesian system. It also works in reverse. UTM can be used with any datum, so it doesn’t give consistent results across datums, meaning the datum must be specified.
Being a conformal mapping system, UTM allows you to use cartesian computation methods on the E/N co-ordinates and your measurements (corrected to allow for the projection distortion), rather than having to do full geodetic calculations for every point and line. In other words, it makes life dramatically simpler for a huge range of surveying and mapping tasks.
In GIS, specifying WGS84 as the datum means you can use GPS data directly. It primarily allows a definition of what you mean by the co-ordinate origin and the orientation of the axes of the reference frame, together with the reference ellipsoid you are using.
Using UTM specifies how lat/long locations are represented as E/N co-ordinates in the database and also on the screen or a printed map.
If you want to use anything other than latitude/longitude to specify locations, you need a map projection. UTM is common for larger GIS projects. WGS84 allows you to have a datum, in the full meaning of the term, and this is projected using the map projection.
A map will have only one coordinate system, either Geographic or Projected in our software’s terminology. For example, the “WGS projection” is a geographic one. A UTM projection is a projected one. Either of these will use only one datum. However, the data on the map could have come from multiple sources, all with unique projections and therefore datums