{"id":36292,"date":"2024-05-30T18:04:00","date_gmt":"2024-05-30T21:04:00","guid":{"rendered":"https:\/\/geartips.club\/blog\/orientation-and-navigation-what-is-magnetic-declination\/"},"modified":"2024-05-30T18:04:00","modified_gmt":"2024-05-30T21:04:00","slug":"orientation-and-navigation-what-is-magnetic-declination","status":"publish","type":"post","link":"https:\/\/geartips.club\/blog\/en\/orientation-and-navigation-what-is-magnetic-declination\/","title":{"rendered":"Orientation and Navigation \u2013 What Is Magnetic Declination?"},"content":{"rendered":"<p>Now it\u2019s time to go a little deeper into the topic and explore <i>magnetic declination<\/i>. The term <i>magnetic declination<\/i> refers to the angle between True North and Magnetic North, just as certain angles have special names\u2014for example, a right angle always measures 90\u00ba.<\/p>\n<div class=\"caixa\">If you\u2019ve been following the articles on Orientation &amp; Navigation here on the Gear Tips blog, remember that I\u2019ve already covered the following topics (linked below for you to revisit!):  <\/p>\n<ul>\n<li><a title=\"Understand the Topographic Map\" href=\"https:\/\/geartips.club\/blog\/orientacao-e-navegacao-1-carta-topografica\/\" target=\"_blank\" rel=\"noopener\">Topographic Map<\/a><\/li>\n<li><a title=\"What Is UTM - Universal Transverse Mercator\" href=\"https:\/\/geartips.club\/blog\/utm-sistema-universal-transverso-de-mercator\/\" target=\"_blank\" rel=\"noopener\">UTM &#8211; Universal Transverse Mercator<\/a><\/li>\n<\/ul>\n<\/div>\n<h2>The three types of north<\/h2>\n<p>There are three types of north represented on topographic maps: (1) True North, (2) Magnetic North, and (3) Grid North (Figure 1 below).  <\/p>\n<p>True North is a human convention, defined as the point where all meridians converge\u2014essentially, the \u201caxis\u201d of the Earth\u2019s rotation at the North Pole. Magnetic North, in turn, represents the alignment of the Earth\u2019s magnetic forces (<a title=\"Earth Magnetism \u2013 Geological Survey of Brazil\" href=\"https:\/\/www.sgb.gov.br\/publique\/SGB-Divulga\/Canal-Escola\/Magnetismo-Terrestre-2623.html\" target=\"_blank\" rel=\"noopener\">suggested reading: Earth Magnetism \u2013 Geological Survey of Brazil<\/a>). Its position changes over the years. In 1831, James Clark Ross was the first to record its location, just north of the Arctic Circle, and in 1904 the Norwegian explorer Roald Amundsen noted that it had shifted position. Finally, there is Grid North\u2014the UTM north discussed in my previous article.<\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"aligncenter size-full wp-image-24228\" src=\"https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-tres-nortes.jpg\" alt=\"The three norths and magnetic declination\" width=\"700\" height=\"485\" srcset=\"https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-tres-nortes.jpg 700w, https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-tres-nortes-300x208.jpg 300w\" sizes=\"(max-width: 700px) 100vw, 700px\" \/><br \/>\n<span class=\"aligncenter\">Figure 1: the three types of north found on topographic maps. GN = Grid North, TN = True North, and MN = Magnetic North (Santos, 1990).<\/span>  <\/p>\n<p>Therefore, it\u2019s important to know the local declination when you want to align your compass with the map. But don\u2019t worry\u2014it\u2019s not as complicated as it sounds. To calculate local declination, simply look at the declination diagram in the map\u2019s legend, as shown in the figure below (Figure 2).<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-24230\" src=\"https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-representacao-carta-topografica.jpg\" alt=\"Representation of magnetic declination on a topographic map\" width=\"392\" height=\"528\" srcset=\"https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-representacao-carta-topografica.jpg 392w, https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-representacao-carta-topografica-223x300.jpg 223w\" sizes=\"(max-width: 392px) 100vw, 392px\" \/><br \/>\n<span class=\"aligncenter\">Figure 2: Magnetic declination represented on the Rio Claro map, IBGE 1969<\/span>  <\/p>\n<h2>Calculating magnetic declination<\/h2>\n<p>In that diagram, you\u2019ll find the map\u2019s declination at the time it was produced, its annual variation, and whether the declination shifts east or west. The legend also indicates the last year the declination was calculated. To update it, multiply the map\u2019s age by its annual variation and add that value to the original declination.  <\/p>\n<p>Let\u2019s use the Rio Claro map (SHEET SF-23-M-I-4), produced by IBGE in 1969, as an example. That year, its declination was 14\u00b038\u2019\u2014fourteen degrees and thirty-eight minutes\u2014west, with an annual variation of 8\u2019 (eight minutes).<\/p>\n<p>Therefore, in 2024, 55 years have passed since the last known declination, resulting in a variation of 440\u2019 (8\u2019 x 55). However, since every degree equals 60 minutes, divide 440 by 60 to convert it into degrees: 7.3333\u00ba, or approximately 7\u00b020\u2019 (7\u00ba x 60 = 420\u2019, with 20\u2019 remaining). Add this to the original declination from 1969: 14\u00b038\u2019 + 7\u00b020\u2019 = 21\u00b058\u2019. (If the total minutes exceed 60, add 1\u00ba and keep the remainder as minutes.) Because the declination moves westward, we must subtract 21\u00b058\u2019 from 0\u00ba\/360\u00ba on the map. Thus, the north direction will be represented by an angle of 338\u00b002\u2019.<\/p>\n<p><strong>Remember these symbols:<\/strong> <strong>\u00ba = degree<\/strong> <strong>\u2018 = minute<\/strong> <strong>\u201c = second<\/strong><\/p>\n<p>In some cases, you\u2019ll also find in the declination diagram the angle between True North and Grid North. This angle arises from the attempt to project the Earth onto a flat surface, as explained in the article on UTM \u2013 Universal Transverse Mercator. Notice in Figure 1 that Grid North follows a straight north-south line that deviates slightly from True North. Fortunately, since this angle is numerically small, it\u2019s usually ignored.<\/p>\n<h2>Using magnetic declination<\/h2>\n<p>There are three ways to use magnetic declination on a map:<br \/>\n1. Drawing new north lines directly on the map.<br \/>\n2. Adjusting the compass (available only on some models).<br \/>\n3. Calculating in the field by adding or subtracting the declination relative to True North.  <\/p>\n<p>From a practical standpoint, the easiest way is to draw the \u201cnew\u201d north on the map. Calculate the declination using the legend\u2019s data, as described above, and with your compass, find that angle relative to the map\u2019s grid lines. Then follow these steps:<\/p>\n<p>1. Set your compass to the calculated declination based on the legend\u2019s data.<br \/>\n2. Place the compass on the map, aligning the north line on the compass dial with one of the map\u2019s grid lines. Ignore the needle for this step.<br \/>\n3. Use a pen to draw the new north lines with the adjusted declination (Figure 3).<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-24231\" src=\"https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-carta-topografica.jpg\" alt=\"Magnetic declination and topographic map\" width=\"700\" height=\"520\" srcset=\"https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-carta-topografica.jpg 700w, https:\/\/geartips.club\/blog\/wp-content\/uploads\/sites\/2\/2024\/05\/declinacao-magnetica-carta-topografica-300x223.jpg 300w\" sizes=\"(max-width: 700px) 100vw, 700px\" \/><br \/>\n<span class=\"aligncenter\">Figure 3: drawing magnetic declination on a topographic map. Ant\u00f4nio Calvo and Paul Colas Rosas, 2007<\/span>  <\/p>\n<p>Pay attention to your compass details, as most models display numerical graduations in increments of two degrees. To simplify fieldwork, you can round the calculated angles and declination values. In the example above, the declination changes from 21\u00ba58\u2019 to 22\u00ba and from 338\u00ba02\u2019 to 338\u00ba.<\/p>\n<p>Now gather all this information\u2014and start practicing! Happy adventures.<\/p>\n<div class=\"caixa\">Watch the videos on <a href=\"https:\/\/geartips.club\/plus\/?s=orienta%C3%A7%C3%A3o\" target=\"_blank\" rel=\"noopener\">orientation and navigation on Gear Tips Plus<\/a>.<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Now it\u2019s time to go a little deeper into the topic and explore magnetic declination. The term magnetic declination refers to the angle between True North and Magnetic North, just as certain angles have special names\u2014for example, a right angle always measures 90\u00ba. If you\u2019ve been following the articles on Orientation &amp; Navigation here on [&hellip;]<\/p>\n","protected":false},"author":1094,"featured_media":29874,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1340,1828],"tags":[1893],"class_list":["post-36292","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-exclusive-articles","category-orientation-and-navigation","tag-orientation-and-navigation"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/posts\/36292","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/users\/1094"}],"replies":[{"embeddable":true,"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/comments?post=36292"}],"version-history":[{"count":0,"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/posts\/36292\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/media\/29874"}],"wp:attachment":[{"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/media?parent=36292"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/categories?post=36292"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/geartips.club\/blog\/en\/wp-json\/wp\/v2\/tags?post=36292"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}