> > Does any one know more about this? Seems if we are using magnetic > north to set instruments, readings can change......... would like to > know your thoughts. Karen >
Using an accurate magnetic compass for surveying is fine but one would need to indicate the magnetic declination for that location on the created map. Now that GPS is used more for surveying, we don't need to rely on the magnetic compass as much. All USGS topo maps will have the declination on it somewhere BUT if it is an old map, the declination will have changed. Will it be so significant that one will get lost? Probably not. What will throw everything for a loop is when the magnetic poles reverse themselves. Not for us but for the animals that can sense the magnetic field and use it for navigation and/or migration. The following site is what I use to determine the current magnetic declination for a location if I need that accuracy for something http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp But yes, due to the fluid nature of the Earth's core, the magnetic poles do wander around.
