Magnetic compasses point to magnetic north, not geographic north (the north pole). Magnetic north is currently located in far northern Canada, and its exact location is constantly, slowly changing.
As you stand facing the direction your compass calls North, true north is usually somewhere to the right or left. The amount of difference is called the declination and it is measured in degrees. The amount of declination depends both on where on the planet you are located, and the year you make the measurement.
Since surveyors used compasses to determine the direction of survey lines the parcels they surveyed were referenced to magnetic north. But as shown above, magnetic north is not the same as true north. When you try to fit an old survey on a modern map you'll find that in many cases the plot must be rotated clockwise or counterclockwise before it will fit. The amount of rotation that must be applied is known as the declination error, and corresponds to the number of degrees of compass declination that were in force when the surveyor made the survey measurements.
How much must your plots be corrected by? That, again, depends on your locale and the time period. A common method for determining the needed correction is to use trial and error correction using parcels that are known to be located on rivers and creeks. Using DeedMapper and its compatible maps you can apply different declination values to parcels in order to determine the 'best fit' value of declination.
Another method is to look at historical values of declination.
NOAA has an interactive map that shows declination changes over time going back hundreds of years.
We've used an early version of their calculator to generate tables of historic declination values for the following U.S. cities in the "metes and bounds" states. We've grouped the cities according to their rough latitude. You can estimate values for other locales by using the values for the nearest city to the east and west of your locale.
Accuracy of the table data is generally within one-half degree (30 minutes), but the presence of natural or artificial disturbances could cause differences of several degrees. Where data are not available "na" is listed. The letter E denotes east declination, W west. For example, 6W means magnetic north lies 6 degrees west of true north.
Surveys in locales having West declinations must be rotated counterclockwise while surveys in locales having East declinations must be rotated clockwise to fit on modern maps accurately. Corrections to within one degree of actual are usually satisfactory. It is generally hard to notice the effect of one degree of rotation or less except on parcels extending over long distances.
Values from 1955 through 1967.5 were derived using the source data of Table 4 of the "Coast and Geodetic Survey Publication 40-2, United States Magnetic Tables for 1960.0". Values subsequent to 1967.5 were calculated from the proper U.S. geomagnetic model obtained from the U.S. Geological Survey Branch of Global Seismology and Geomagnetism. Declination values for 1970 are from the U.S. polynomial model which produced map I-911, Magnetic Declination in the United States Epoch 1975. Declination values for 1975 are from the U.S. polynomial model which produced map I-1283, Magnetic Declination in the United States Epoch 1980. Declination values from 1980 to the present are derived from the spherical harmonic models USCON80, USCON85, and USCON90.
------------------------------------------------------- LAT: 44 DEG 18 MIN NORTH LONG: 69 DEG 46 MIN WEST CITY & STATE: Augusta, ME ------------------------------------------------------- YEAR DECLINATION 1750 9 56 WEST 1760 9 37 1770 9 26 1780 9 28 1790 9 36 1800 9 58 1810 10 26 1820 11 3 1830 11 45 1840 12 30 1850 13 18 1860 14 3 1870 14 34 1880 15 3 1890 15 21 1900 15 46 1910 16 39 1920 17 25 1930 18 5 1940 18 21 1950 18 17 1960 18 12 1970 17 57 1980 17 52 1990 17 30 2000 17 28 ------------------------------------------------------- LAT: 42 DEG 21 MIN NORTH LONG: 71 DEG 3 MIN WEST CITY & STATE: Boston, MA ------------------------------------------------------- YEAR DECLINATION 1750 7 42 WEST 1760 7 16 1770 6 59 1780 6 51 1790 6 52 1800 7 5 1810 7 25 1820 7 53 1830 8 29 1840 9 11 1850 9 56 1860 10 38 1870 11 12 1880 11 45 1890 12 9 1900 12 40 1910 13 36 1920 14 23 1930 15 7 1940 15 24 1950 15 22 1960 15 24 1970 15 24 1980 15 39 1990 15 42 2000 15 54 ------------------------------------------------------- LAT: 41 DEG 46 MIN NORTH LONG: 72 DEG 40 MIN WEST CITY & STATE: Hartford, CT ------------------------------------------------------- YEAR DECLINATION 1750 6 31 WEST 1760 5 58 1770 5 34 1780 5 18 1790 5 13 1800 5 17 1810 5 31 1820 5 53 1830 6 25 1840 7 4 1850 7 46 1860 8 27 1870 9 4 1880 9 41 1890 10 8 1900 10 42 1910 11 35 1920 12 21 1930 13 5 1940 13 21 1950 13 19 1960 13 24 1970 13 32 1980 14 1 1990 14 20 2000 14 43 ------------------------------------------------------- LAT: 43 DEG 9 MIN NORTH LONG: 77 DEG 36 MIN WEST CITY & STATE: Rochester, NY ------------------------------------------------------- YEAR DECLINATION 1750 5 9 WEST 1760 4 25 1770 3 43 1780 3 9 1790 2 44 1800 2 30 1810 2 27 1820 2 36 1830 2 56 1840 3 26 1850 4 0 1860 4 38 1870 5 18 1880 6 7 1890 6 45 1900 7 23 1910 8 5 1920 8 47 1930 9 28 1940 9 37 1950 9 27 1960 9 30 1970 9 46 1980 10 33 1990 11 11 2000 11 52 ------------------------------------------------------- LAT: 40 DEG 45 MIN NORTH LONG: 73 DEG 59 MIN WEST CITY & STATE: New York, NY ------------------------------------------------------- YEAR DECLINATION 1750 5 10 WEST 1760 4 32 1770 4 2 1780 3 41 1790 3 30 1800 3 30 1810 3 38 1820 3 56 1830 4 24 1840 5 0 1850 5 40 1860 6 20 1870 6 58 1880 7 37 1890 8 7 1900 8 42 1910 9 32 1920 10 16 1930 11 0 1940 11 14 1950 11 13 1960 11 22 1970 11 40 1980 12 20 1990 12 56 2000 13 29 ------------------------------------------------------- LAT: 39 DEG 56 MIN NORTH LONG: 75 DEG 9 MIN WEST CITY & STATE: Philadelphia, PA ------------------------------------------------------- YEAR DECLINATION 1750 4 13 WEST 1760 3 35 1770 3 3 1780 2 37 1790 2 23 1800 2 18 1810 2 22 1820 2 36 1830 3 0 1840 3 31 1850 4 8 1860 4 45 1870 5 23 1880 6 2 1890 6 34 1900 7 9 1910 7 54 1920 8 35 1930 9 17 1940 9 29 1950 9 28 1960 9 40 1970 10 5 1980 10 56 1990 11 42 2000 12 24 ------------------------------------------------------- LAT: 39 DEG 17 MIN NORTH LONG: 76 DEG 36 MIN WEST CITY & STATE: Baltimore, MD ------------------------------------------------------- YEAR DECLINATION 1750 2 54 WEST 1760 2 15 1770 1 40 1780 1 12 1790 0 54 1800 0 45 1810 0 46 1820 0 57 1830 1 17 1840 1 46 1850 2 21 1860 2 58 1870 3 38 1880 4 18 1890 4 52 1900 5 29 1910 6 12 1920 6 49 1930 7 29 1940 7 39 1950 7 37 1960 7 51 1970 8 23 1980 9 23 1990 10 19 2000 11 9 ------------------------------------------------------- LAT: 40 DEG 26 MIN NORTH LONG: 80 DEG 0 MIN WEST CITY & STATE: Pittsburgh, PA ------------------------------------------------------- YEAR DECLINATION 1750 NA 1760 NA 1770 NA 1780 NA 1790 0 42 EAST 1800 0 58 1810 1 4 1820 1 0 1830 0 45 1840 0 20 1850 0 10 WEST 1860 0 45 1870 1 24 1880 2 6 1890 2 46 1900 3 23 1910 3 57 1920 4 28 1930 5 4 1940 5 8 1950 5 0 1960 5 12 1970 5 46 1980 6 55 1990 7 58 2000 8 56 ------------------------------------------------------- LAT: 37 DEG 32 MIN NORTH LONG: 77 DEG 26 MIN WEST CITY & STATE: Richmond, VA ------------------------------------------------------- YEAR DECLINATION 1750 1 22 WEST 1760 0 44 1770 0 11 1780 0 16 EAST 1790 0 34 1800 0 43 1810 0 44 1820 0 35 1830 0 16 1840 0 11 WEST 1850 0 45 1860 1 21 1870 2 1 1880 2 40 1890 3 15 1900 3 51 1910 4 31 1920 5 2 1930 5 38 1940 5 47 1950 5 47 1960 6 6 1970 6 47 1980 7 57 1990 9 0 2000 9 58 ------------------------------------------------------- LAT: 37 DEG 16 MIN NORTH LONG: 79 DEG 56 MIN WEST CITY & STATE: Roanoke, VA ------------------------------------------------------- YEAR DECLINATION 1750 0 6 WEST 1760 0 34 EAST 1770 1 10 1780 1 40 1790 2 3 1800 2 18 1810 2 22 1820 2 17 1830 2 3 1840 1 40 1850 1 11 1860 0 37 1870 0 1 WEST 1880 0 41 1890 1 19 1900 1 54 1910 2 26 1920 2 50 1930 3 20 1940 3 24 1950 3 20 1960 3 40 1970 4 26 1980 5 44 1990 6 54 2000 8 0 ------------------------------------------------------- LAT: 38 DEG 21 MIN NORTH LONG: 81 DEG 37 MIN WEST CITY & STATE: Charleston, WV ------------------------------------------------------- YEAR DECLINATION 1750 0 11 EAST 1760 0 51 1770 1 30 1780 2 3 1790 2 30 1800 2 48 1810 2 56 1820 2 53 1830 2 42 1840 2 21 1850 1 54 1860 1 21 1870 0 44 1880 0 4 1890 0 36 WEST 1900 1 11 1910 1 39 1920 2 2 1930 2 30 1940 2 31 1950 2 25 1960 2 41 1970 3 25 1980 4 45 1990 5 52 2000 6 58 ------------------------------------------------------- LAT: 38 DEG 2 MIN NORTH LONG: 84 DEG 29 MIN WEST CITY & STATE: Lexington, KY ------------------------------------------------------- YEAR DECLINATION 1750 NA 1760 NA 1770 NA 1780 NA 1790 NA 1800 4 29 EAST 1810 4 40 1820 4 43 1830 4 37 1840 4 21 1850 3 58 1860 3 28 1870 2 54 1880 2 14 1890 1 32 1900 0 59 1910 0 39 1920 0 23 1930 0 1940 0 5 1950 0 13 1960 0 4 WEST 1970 0 51 1980 2 16 1990 3 21 2000 4 30 ------------------------------------------------------- LAT: 35 DEG 46 MIN NORTH LONG: 77 DEG 38 MIN WEST CITY & STATE: Raleigh, NC ------------------------------------------------------- YEAR DECLINATION 1750 0 22 WEST 1760 0 14 EAST 1770 0 46 1780 1 11 1790 1 29 1800 1 37 1810 1 37 1820 1 29 1830 1 10 1840 0 44 1850 0 12 1860 0 24 WEST 1870 1 4 1880 1 41 1890 2 16 1900 2 51 1910 3 30 1920 3 58 1930 4 31 1940 4 40 1950 4 42 1960 5 5 1970 5 53 1980 7 9 1990 8 14 2000 9 17 ------------------------------------------------------- LAT: 35 DEG 35 MIN NORTH LONG: 82 DEG 33 MIN WEST CITY & STATE: Asheville, NC ------------------------------------------------------- YEAR DECLINATION 1750 1 42 EAST 1760 2 21 1770 2 57 1780 3 30 1790 3 55 1800 4 13 1810 4 21 1820 4 20 1830 4 10 1840 3 51 1850 3 26 1860 2 54 1870 2 18 1880 1 38 1890 0 58 1900 0 26 1910 0 1 1920 0 12 WEST 1930 0 33 1940 0 31 1950 0 27 1960 0 50 1970 1 43 1980 3 9 1990 4 17 2000 5 29 ------------------------------------------------------- LAT: 35 DEG 57 MIN NORTH LONG: 83 DEG 55 MIN WEST CITY & STATE: Knoxville, TN ------------------------------------------------------- YEAR DECLINATION 1750 2 11 EAST 1760 2 50 1770 3 28 1780 4 2 1790 4 29 1800 4 48 1810 4 58 1820 4 59 1830 4 52 1840 4 35 1850 4 11 1860 3 41 1870 3 6 1880 2 26 1890 1 45 1900 1 13 1910 0 53 1920 0 42 1930 0 23 1940 0 28 1950 0 33 1960 0 11 1970 0 42..WEST 1980 2 10 1990 3 17 2000 4 29 ------------------------------------------------------- LAT: 36 DEG 9 MIN NORTH LONG: 86 DEG 46 MIN WEST CITY & STATE: Nashville, TN ------------------------------------------------------- YEAR DECLINATION 1750 NA 1760 NA 1770 NA 1780 NA 1790 NA 1800 6 10 EAST 1810 6 24 1820 6 31 1830 6 29 1840 6 18 1850 5 59 1860 5 32 1870 5 2 1880 4 22 1890 3 40 1900 3 9 1910 2 57 1920 2 51 1930 2 36 1940 2 45 1950 2 54 1960 2 34 1970 1 43 1980 0 14 1990 1 2 2000 2 13 ------------------------------------------------------- LAT: 34 DEG 0 MIN NORTH LONG: 81 DEG 2 MIN WEST CITY & STATE: Columbia, SC ------------------------------------------------------- YEAR DECLINATION 1750 1 41 EAST 1760 2 17 1770 2 52 1780 3 21 1790 3 43 1800 3 57 1810 4 2 1820 3 58 1830 3 46 1840 3 25 1850 2 58 1860 2 26 1870 1 49 1880 1 9 1890 0 32 1900 0 1 WEST 1910 0 29 1920 0 42 1930 1 4 1940 1 4 1950 1 3 1960 1 30 1970 2 27 1980 3 53 1990 5 3 2000 6 17 ------------------------------------------------------- LAT: 33 DEG 45 MIN NORTH LONG: 84 DEG 23 MIN WEST CITY & STATE: Atlanta, GA ------------------------------------------------------- YEAR DECLINATION 1750 2 53 EAST 1760 3 30 1770 4 6 1780 4 40 1790 5 6 1800 5 26 1810 5 36 1820 5 38 1830 5 32 1840 5 17 1850 4 55 1860 4 25 1870 3 52 1880 3 12 1890 2 32 1900 2 2 1910 1 45 1920 1 41 1930 1 28 1940 1 34 1950 1 38 1960 1 13 1970 0 15 1980 1 14 WEST 1990 2 23 2000 3 38
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