These are degree based spherical (aka polar) coordinates. The distance and bearing between two points need special care as Great-Circle calculations must be used. If you want a highly inaccurate cheat, you can remember that there are 1852m in a nautical mile, and 60 nautical miles in a degree of latitude (111km). The width of a degree longitude varies as the cosine of the latitude. So at the equator it is 111km wide and by the poles it is nil. Navigation charts and GPSs will typically churn out lat/lon coordinates. Now-a-days (since 1984) this will be used together with the WGS84 datum. This datum defines the 0,0,0 x,y,z orgin of the Earth at its centre of mass and the difference between a perfect sphere and the lumpy ellipsoid we actually live on. In general the centre-spot and gravitational lumpiness wasn’t very well known before we sent up satellites, so older dautms will vary widely while newer versions will only vary be a few cm. (besides the 1984 one some common modern datums are 1996 and 2000 versions) To avoid confusion make sure your handheld GPS is set to use WGS84. As tempting as it may be, don’t ever mess with a ship’s navigation GPS without the skipper looking on, they will have set it up to work a certain way and will be expecting that to be the case. Woe be the student who invokes the captain’s ire. The common use is to put latitude first, but keep in mind that when plotting or converting coordinates this puts the northing first, i.e. ‘y x’. While it may seem obvious, the conversion between degrees, minutes, and seconds always seems to lead to mass confusion, often because what was used wasn’t written down. (e.g. instead of punctuation just a string of numbers was written down) So always write the little =o= degree sign, the ‘ minute sign, and ‘ second sign, and a clear decimal point or you’ll regret it. It helps to also create a waypoint in the GPS whenever you have to write one down. You can download it later which is less work than transcribing and less error prone after a long day of staring at a spreadsheet. These are typically meters based so distance and area calculations are much much simpler to work with. Unlike lat/lon usually they are limited in their range, the further you go away from the centre the more distortion is introduced. Coordinates are usually referred to as ‘eastings’ and ‘northings’ and their values will typically be in the millions. Each map projection will have its own set of transform parameters. Often your GPS data will come with a .prj file with ‘Well Known Text’ (WKT) describing the projection. Just like in biology there are often many names for the same thing, so the European Petroleum Survey Group (EPSG) decided to give each unique projection its own ID code to help ease the pain of translation. If your software supports it EPSG codes are the easiest way of identifying which coordinate system you are actually talking about. If you prefer to use something less costly than Matlab, Octave is Free and runs in a manner ‘not dissimilar’. Python is an easy to use and learn, yet powerful, scripting language which is quickly becoming the de facto standard for scientific programming. Control of map projections in QGIS is somewhat free-form. It will let you load up the data first and worry about projections later. Control of map projections in GRASS can be a bit more strict than users of other GIS mapping software may be used to. GRASS will try to stop you from doing the wrong thing projection-wise. So you may see more error messages up front but your data is less likely to get silently broken somewhere along the way. This is simply a different compromise based on a different set of values. Control of map projections in Arc is somewhat free-form. It will let you load up the data first and worry about projections later. Source.