Making Sense Out of North

Second article in a seven-part series

Many of us who would go messing about in the backcountry are "north challenged." Sure, we know a compass points north and we know that most maps are drawn "north up," so why doesn't our compass always agree with the map? First, the needle on a compass doesn't point to a big magnetic rock somewhere in the Arctic as many people believe. Instead, it aligns with an invisible magnetic field that covers the earth. This force field moves all the time but, lucky for us, the change happens slowly and predictably. At least for our navigation needs.

We call the direction to which a compass points magnetic north. We need to know where magnetic north is so we can find true north, because that's the north that's up on our maps.If we think of the earth as a round ball—it isn't, but picture it anyway—and we could turn it in our hands, the first thing we'd notice is that there is no start or finish point. If the people who believed the earth is flat had been right, we wouldn't have had a problem because there would have been corners to start from. But they were wrong, and the scientists of the day had to do something about it if we were going to have accurate maps and reliable navigation.

Let There Be Zero!
It wasn't an easy fight but the geographers finally agreed to draw two zero lines around the globe. One at the equator divided north from south. The second divided east from west and ran from the North Pole to the South Pole through Greenwich, England. They called the second line the prime meridian.

All of these meridians converge at the North and South Poles.

Magnetic vs. True
It's easy to see that there's a difference between where our compass points and the true North Pole—it's called declination. But that pesky magnetic force field isn't going to let us off easy, because declination doesn't follow straight lines and isn't equal around the world or even across North America.

If we hiked, compass in hand, from the tip of Florida, across Lakes Michigan and Superior (quite a hike, that) and on up to the Arctic Ocean, the needle would be pointing toward true north. That route is called the agonic line and it's the only place in North America where magnetic north is the same as true north. But few of us hike, bike, or canoe along that route, so we have to put up with the difference between magnetic and true. As the chart shows, this varies widely the farther east and west we travel.