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The Content of the Site Plan
Published in Robert M. Sanford, Environmental Site Plans and Development Review, 2017
True and magnetic north arrows are commonly shown on site plans. By convention, north arrow points are placed to the right or top of the plan. In some cases, there is an assumed north placed straight up on the site plan regardless of the real north direction. A compass normally does not point to true north. It points to magnetic north. The angle between magnetic north and the true north direction is called the magnetic declination. This declination changes over time, thus making it necessary to adjust the orientation on older maps and also reiterate why the date of the map is important. Magnetic north is close to 15 degrees west of true north. A third north that may be on a site plan is called “grid north,” referring to the grid lines, usually Universal Transverse Mercator (UTM) on a map. Magnetic fields fluctuate over the Earth and every five years a new International Geomagnetic Reference Field (IGRF) is generated to produce accurate calculations of angles of declination.
The Earth–Sun Relationship
Published in Matt Fajkus, Dason Whitsett, Architectural Science and the Sun, 2018
Magnetic declination is the angle at any location between magnetic north and true north. Magnetic declination varies considerably from place to place and also changes as the magnetic pole moves. Figure 2.8 shows contours of magnetic declination for North America in 2010 based on models from NOAA.4Table 2.4 lists the magnetic declination for some major cities worldwide. Positive magnetic declination indicates magnetic north is east of true north. If the magnetic declination is negative, magnetic north is west of true north. For compass readings to be useful, it is essential that they be adjusted for magnetic declination (Figure 2.9).
Solar Insolation
Published in Dorothy Gerring, Renewable Energy Systems for Building Designers, 2023
Magnetic declination is the variation, measured in a horizontal plane, between magnetic north and true north. Compass readings need to be corrected for this difference because it can be very large. Figure 5.13 shows a world magnetic declination map from the year 2021. The green line shows where magnetic north and true north align. The curving lines are called isogonic lines and each of the blue and red lines are indicating how much magnetic variation, moving away by degrees, is occurring compared to the location of true north. The exact location and value of the isogonic lines change over time and can be very unreliable around the poles.
Multi-disciplinary ore deposit exploration in Sonqor, northwest Iran
Published in Australian Journal of Earth Sciences, 2021
S. Niroomand, D. Poreh, A. Kananian
We applied a reduction to pole (RTP) filter with magnetic declination/variation, and magnetic deviation of 51.2° and 3.19°, respectively, to the magnetic fields so the shapes of anomalies are slightly deteriorated to the northern parts.