Ahead of fieldwork for my thesis I asked what kind of GPS device is recommmendable. A number of fellow geobloggers replied with valuable advise. I actually went and bought a GPS ahead of fieldwork. Now I am a proud owner of a GPSmap 60CSx. The device has fullfilled all expectations in terms of durability, endurance and accuracy under not perfect conditions. The batteries last for 3 days of work or more. Dropping it on rock doesn't cause a scratch and signal reception under dense tree cover is excellent. As a matter of fact I still had a signal when entering underground caves. Well, at least for the first two or three meters. But I don't want to make a commercial here. Fellow geobloggers will know, non-trained readers might wonder though what I do with a GPS device. The idea is pretty simple. It allows to rapidly map and document geological relationships in the field with sufficient accuracy. Mapping lithological borders i.e. becomes a piece of cake. Find the contact in 3 or 4 locations, take a measurement of Easting and Northing, if possible also take a dip measurement with your geologists compass, and you are done. At least in principle. You don't necessarily need the expensive GPS device I decided to buy. A price of 260 Euros is not cheap. There are cheaper alternatives or even more expensive ones with a great variety of additional gadgets.
Using a GPS is easy. If you do not get training at University the documentation should allow you to catch on easily. The basic steps are simple. When the accurate position is your main or only interest, as it may be for most geological fieldwork, there is not much to do. After activating the device give it a moment to acquire a satellite signal. Depending on the location and ground conditions this should not take longer than 1 minute with a good device. Next select the position format and map datum. Usually these are hidden in the units or settings options of your device. In the most simpliest sense the position format determines the way how you write down your coordinates. As the Earth is an irregular globe your need a projection to realistically depict the surface in a flat, 2D map. One of the most common formats is the UTM (Universal Transverse Mercator) format that devides the surface into boxes. The map datum is the reference system. Because our planet is not a perfect globe you need a different model of the surface depending on your position. A model that best fits the real shape of the planet. A commonly used datum is the WGS84. Depending on your location you may wish to use another format and datum. In Germany you will still frequently encounter the Gauss-Krüger-coordinate system combined with the Potsdam-Datum or the Bessel-Ellipsoid (Bessel 1841). It fits the Geoid in Europe exceptionally well.
Having decided on your position format and map datum you can start mapping. Either simply noting the coordinates into your fieldbook or saving way points for download in the evening. When using way points remember to always save the way point and not to forget one. When working on large areas way points will make it easier to track back your movements.