Field notes
Blog
Grid technique, land navigation and survival reference, written the way the manuals are.
01 ·
Grid North, Magnetic North and True North
Three norths, three different directions, and the angles between them. What the declination diagram on a map sheet is telling you, how to convert an azimuth from one reference to another, and which north each of your instruments actually reports.
5 min read
02 ·
What Is Magnetic Declination and Why It Matters
Magnetic declination is the angle between true north and where your compass points. How much error it causes, why it changes with location and year, where the zero line runs, and how to get a current value for where you are standing.
5 min read
03 ·
What Is WGS-84?
WGS-84 is the datum every GPS fix is reported on. What a datum actually is, how far a coordinate moves when the datum is wrong, and why your GPS altitude disagrees with the elevation printed on the map.
5 min read
04 ·
UTM Zones Explained
How the 60 UTM zones are numbered, how to work out your zone from a longitude, what the central meridian and scale factor do, and the irregular zones around Norway and Svalbard that break the 6 degree rule.
6 min read
05 ·
MGRS vs UTM: What Is the Difference?
MGRS and UTM describe the same point on the same projection, but they label it differently. A worked comparison of both formats, the false easting and northing that trip people up, and how to tell a hemisphere letter from a latitude band.
6 min read
06 ·
How to Read MGRS Coordinates
A field-manual walkthrough of the Military Grid Reference System: grid zone, 100 km square, and the easting/northing digits, plus how to read a grid to 1 metre and avoid the mistakes that put you in the wrong square.
4 min read