How To Calculate Magnetic Declination On A Topographic Map
How to calculate magnetic declination on a topographic map
Calculate the difference in years the present year the year indicated on the map multiply the difference in years by the mean annual average. When using a topographic map true north is always at the top of the map.
Magnetic Declination
Topographical maps there is a symbol called the magnetic declination.
The collar of usgs topographic maps shows the magnetic declination at the center of the map the year that the map was made. Determining magnetic declination and dip the angle between the true meridian and the magnetic meridian is magnetic declina tion. Draw a straight line from your starting point to the end point. The center line with the star above represents the direction of true geographic north.
Check the scale of the map remember sa topographic maps have a scale of 1 50 000. Geography grade 12 www learnxtra co za brought to you by page 8 find the magnetic declination on the map and the year it was taken it is found on the right hand side of the map. To measure the bearing from one point to the next the protractor must be aligned so that 0 point to the top of the map true north. No matter how far magnetic north has separated from true north finding magnetic declination the angle between magnetic north and true north can be found using the legend on your topographic map as well as by using tools like the noaa magnetic declination calculator.
True north points to the geographic north pole or the northern location of the earth s. After finding the declination on the map you need to. To adjust for declination first reference your map. It is usually printed on the map to the left of the scale bar at the bottom of a usgs 7 5 quadrangle.
To calculate magnetic declination accurately you will need to. In these quadrants you add westerly attraction and subtract easterly attraction to the compass bearing to get the magnetic bearing. That s important information for anyone who is using the map and a compass to navigate. Geostac home field exercises.
Magnetic declination is the angular difference between geographic north true north and magnetic north. Noaa has an online calculator for estimating the declination at any longitude latitude on a specific date. This angle is properly called grid declination. Magnetic declination is the difference between true north the axis around which the earth rotates and magnetic north the direction the needle of a compass will point.
The line coming of to the right represents the direction. However the diagram on the topographic map sheet gives the value of the angle between magnetic north and grid north which is referenced to the grid lines shown on the map. Topographic maps field exercises exercise 1 exercise 2 exercise 3 exercise 4. This change is known as the magnetic declination.
The symbol is used in conjunction with a compass for navigational purposes. Declination is defined as the angle between magnetic north and the true north.
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