地磁気とは

地球は巨大な磁石になっており、北極の磁石のS極と、南極のN極との間に磁気が分布しており、これを地磁気と呼びます。

地磁気についての詳細は、 国土地理院による解説( http://vldb.gsi.go.jp/sokuchi/geomag/menu_01/ )をご参照ください。

方位磁針(コンパス)は、地磁気によって概ね北を指します。

しかし、厳密には下図の偏角(Declination)の示すように、場所によってずれが生じています。

 

偏角の補正方法については、ApplicationNoteの偏角補正をご参照ください。

※ 表のデータは、NOAANGDC Geomagnetic Calculatorsにより計算されました。

 

※ 表にない都市や任意の緯度経度での地磁気の値も、NGDC Geomagnetic Calculatorsで計算することが出来ます。

Examples of magnetifc field at world major cities. (Oct. 2012)
City Latitude Longitude Declination Inclination Horizontal Intensity Total Field
Tokyo (Japan) N 35° 40' 59" E 139° 48' 32" -7° 5' 54" 49° 20' 41" 30,207.63 nT 46,365.81 nT
Sapporo (Japan) N 43° 3' 18" E 141° 20' 46" -9° 17' 3" 57° 33' 54" 26,848.38 nT 50,058.42 nT
Fukuoka (Japan) N 33° 34' 48" E 130° 24' 7" -7° 0' 1" 48° 21' 5" 31,756.98 nT 47,786.56 nT
New York (United States) N 40° 42' 28" W 73° 54' 19" -13° 6' 38" 66° 56' 4" 20,463.68 nT 52,231.90 nT
Los Angeles (United States) N 34° 0' 0" W 118° 15' 0" 12° 29' 7" 58° 49' 25" 24,512.49 nT 47,351.15 nT
San Francisco (United States) N 37° 47' 45" W 122° 22' 48" 14° 2' 33" 61° 15' 30" 23,476.35 nT 48,821.39 nT
Chicago (United States) N 41° 49' 36" W 87° 38' 29" -3° 39' 13" 69° 27' 12" 19,061.93 nT 54,312.25 nT
Houston (United States) N 29° 46' 19" W 95° 24' 26" 3° 3' 12" 58° 59' 14" 24,534.78 nT 47,619.03 nT
Honolulu (United States) N 21° 19' 44" W 157° 51' 43" 9° 42' 52" 37° 57' 58" 27,644.97 nT 35,065.78 nT
Atlanta (United States) N 33° 47' 46" W 84° 20' 56" -4° 46' 39" 62° 50' 16" 22,749.64 nT 49,833.75 nT
Montreal (Canada) N 45° 32' 28" W 73° 39' 13" -14° 47' 6" 70° 30' 59" 18,130.41 nT 54,358.14 nT
Vancouver (Canada) N 49° 16' 27" W 122° 57' 47" 17° 5' 41" 70° 21' 25" 18,433.38 nT 54,834.91 nT
Mexico city (Mexico) N 19° 25' 37" W 99° 7' 39" 5° 13' 4" 47° 13' 11" 27,745.27 nT 40,850.71 nT
Sao Paulo (Brazil) S 23° 34' 52" W 46° 37' 23" -20° 43' 24" -36° 5' 36" 18,568.52 nT 22,979.19 nT
London (United Kingdom) N 51° 29' 16" W 0° 10' 41" -1° 19' 40" 66° 26' 16" 19,442.96 nT 48,638.62 nT
Paris (France) N 48° 52' 55" E 2° 25' 59" -0° 10' 42" 64° 19' 6" 20,780.42 nT 47,950.83 nT
Milan (Italy) N 45° 28' 23" E 9° 11' 24" 1° 49' 31" 61° 31' 59" 22,516.36 nT 47,238.78 nT
Rome (Italy) N 41° 52' 48" E 12° 31' 12" 2° 28' 1" 58° 3' 39" 24,482.40 nT 46,279.03 nT
Vienna (Austria) N 48° 12' 8" E 16° 19' 16" 3° 34' 2" 64° 29' 36" 20,891.64 nT 48,515.49 nT
Brussels (Belgium) N 50° 50' 13" E 4° 22' 5" 0° 17' 34" 66° 4' 33" 19,707.46 nT 48,597.01 nT
Amsterdam (Netherlands) N 52° 22' 23" E 4° 53' 41" 0° 21' 31" 67° 19' 52" 18,899.32 nT 49,037.83 nT
Berlin (Germany) N 52° 30' 59" E 13° 19' 39" 3° 1' 50" 67° 48' 57" 18,678.88 nT 49,469.32 nT
Dusseldolf (Germany) N 51° 14' 28" E 6° 47' 53" 1° 2' 46" 66° 30' 48" 19,452.08 nT 48,809.07 nT
Geneve (Switzerland) N 46° 12' 7" E 6° 8' 2" 1° 2' 42" 62° 2' 39" 22,169.94 nT 47,291.64 nT
Stockholm (Sweden) N 59° 19' 52" E 17° 59' 29" 5° 11' 54" 72° 36' 39" 15,323.74 nT 51,273.74 nT
Moscow (Russia) N 55° 45' 0" E 37° 42' 0" 10° 23' 34" 71° 18' 54" 16,761.18 nT 52,318.83 nT
Beijing (China) N 39° 54' 22" E 116° 23' 17" -6° 32' 29" 58° 38' 55" 28,304.37 nT 54,401.46 nT
Shanghai (China) N 31° 14' 53 E 121° 28' 23" -5° 31' 51" 46° 39' 43" 33,369.82 nT 48,622.75 nT
Dalian (China) N 39° 1' 54" E 121° 35' 54" -7° 36' 13" 56° 50' 44" 28,967.70 nT 52,967.32 nT
Guangzhou (China) N 23° 5' 46" E 113° 17' 37" -2° 31' 18" 34° 5' 7" 37,633.56 nT 45,440.00 nT
Nanjing (China) N 32° 2' 53" E 118° 46' 8" -5° 16' 13" 48° 13' 0" 33,062.56 nT 49,619.88 nT
Qingdao (China) N 36° 8' 54" E 120° 26' 3" -6° 36' 29" 53° 30' 38" 30,701.42 nT 51,627.18 nT
Taipei (Taiwan) N 25° 2' 6" E 121° 30' 24" -3° 58' 45" 36° 44' 32" 36,184.76 nT 45,155.67 nT
Seoul (South Korea) N 37° 32' 32" E 126° 56' 7" -8° 0' 12" 54° 6' 16" 29,852.31 nT 50,915.72 nT
Singapore (Singapore) N 1° 16' 8" E 103° 49' 54" 0° 12' 11" -15° 4' 2" 40,664.68 nT 42,112.46 nT
Manila (Philippines) N 14° 37' 0" E 120° 58' 1" -1° 36' 17" 16° 22' 58" 39,194.64 nT 40,853.32 nT
Kuala Lumpur (Malaysia) N 3° 9' 0" E 101° 42' 29" -0° 6' 56" -10° 55' 39" 41,071.57 nT 41,830.03 nT
Bangkok (Thailand) N 13° 45' 0" E 100° 31' 0" -0° 40' 57" 14° 24' 38" 41,071.75 nT 42,405.93 nT
Ho Chi Minh City (Vietnam) N 10° 45' 33" E 106° 39' 45" -0° 21' 49" 7° 43' 2" 41,121.44 nT 41,497.29 nT
Jakarta (Indonesia) S 6° 10' 0" E 106° 48' 0" 0° 43' 58" -30° 40' 21" 38,353.01 nT 44,591.49 nT
New Delhi (India) N 28° 34' 7" E 77° 13' 0" 0° 51' 51" 44° 24' 8" 34,187.01 nT 47,851.13 nT