22:
779:. This change in flattening is about 0.1 mm, a difference so small that computational programs often do not distinguish between the two ellipsoids. However, due to differences in how the reference ellipsoids are centered and oriented, coordinates in the two datums differ from each other by amounts on the order of a meter over much of the United States. Each datum has undergone refinements with more accurate and later measurements. One well-known difference is the placement of the center of the Earth, with the two systems differing by about 2.2 metres (7.2 ft).
44:
728:
652:, the ellipsoid that best approximates its shape varies region by region across the world. Clarke 1866, and North American Datum of 1927 with it, were surveyed to best suit North America as a whole. Likewise, historically, most regions of the world used ellipsoids measured locally to best suit the vagaries of Earth's shape in their respective locales. While ensuring the most accuracy locally, this practice makes integrating and disseminating information across regions troublesome.
786:, whereas WGS 84 is defined with respect to the average of stations all over the world. Thus the two systems naturally diverge over time. For much of the United States the relative rate is on the order of 1 to 2 cm per year. Hawaii and the coastal portions of central and southern California west of the
798:
The United States
National Spatial Reference System NAD 83(2011/MA11/PA11) epoch 2010.00, is a refinement of the NAD 83 datum using data from a network of very accurate GPS receivers at Continuously Operating Reference Stations (CORS). The NAD 83(2011) describes the main North American
735:
A point having a given latitude and longitude in NAD 27 may be displaced on the order of many tens of meters from another point having the identical latitude and longitude in NAD 83, so it is important to specify the datum along with the coordinates. The North
American Datum of 1927 is
533:
The North
American Datum of 1927 (NAD 27) was based on surveys of the entire continent from a common reference point that was chosen in 1901, because it was as near the center of the contiguous United States as could be calculated: It was based on a
740:
in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The North
American Datum of 1983 is based on a newer defined spheroid (GRS 80); it is an Earth-centered (or
566:) to be 255°28′14.52″ from north. The latitude and longitude of every other point in North America is then based on its distance and direction from Meades Ranch: If a point was X meters in azimuth Y degrees from Meades Ranch, measured on the
639:
topographic maps were published in NAD 27 and many major projects by the United States Army Corps of
Engineers and other agencies were defined in NAD 27, so the datum remains important, despite more refined datums being available.
632:= 20,855,121 British feet. The conversion to meters uses Clarke's 1865 inch-meter ratio of 39.370432. The length of a foot or meter at the time could not practically be benchmarked to better than about 0.02 mm.
675:, are generally not the best fit for any given region, a need for the closest fit largely evaporates when a global survey is combined with computers, databases, and software able to compensate for local conditions.
521:
of 1866. It was fitted to data previously collected for regional datums, which by that time had begun to overlap. In 1913, Canada and Mexico adopted that datum, so it was also renamed the North
American Datum.
751:
provides a converter between the two systems. The practical impact is that if you use a modern GPS device set to work in NAD 83 or WGS 84 to navigate to NAD 27 coordinates (as from a
472:, two North American Datums are in use for making lateral or "horizontal" measurements: the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). Both are
667:
applications, it became feasible to acquire information referred to a single global ellipsoid. This is because satellites naturally deal with Earth as a monolithic body. Therefore, the
671:
ellipsoid was developed for best approximating the Earth as a whole, and it became the foundation for the North
American Datum of 1983. Though GRS 80 and its close relative,
1127:
NAD 83: What Is It and Why You Should Care by Dane E. Ericksen, P.E., Hammett & Edison, Inc., Consulting
Engineers. 1994 SBE National Convention and World Media Expo.
848:
These new reference frames are intended to be easier to access and to maintain than NAD 83 and NAVD 88, which rely on physical survey marks that deteriorate over time.
775:
The definition of NAD 83(1986) is based on the GRS 80 spheroid, as was WGS 84, so many older publications indicate no difference. WGS 84 subsequently changed to a
547:
403:
530:
As more data were gathered, discrepancies appeared, so the datum was recomputed in 1927, using the same spheroid and origin as its predecessor.
460:
network in North
America. A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. In
934:
225:
1129:
393:
361:
371:
1153:
507:
857:
826:
484:
351:
830:
1098:
737:
551:
132:
25:
1016:
820:
431:
881:
1061:
636:
217:
570:
518:
233:
1158:
558:
to be 39°13′26.686″ north latitude, 98°32′30.506″ west longitude. NAD 27 is oriented by declaring the
845:
model is the product of the
Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project.
562:
from Meades Ranch to Waldo Station (also in Osborne County, about 4.5 mi (7.2 km) northwest of
829:(NAVD 88), are set to be replaced with a new geometric reference frame and geopotential datum based on
834:
473:
196:
1062:"How to Transition to the United States 2022 National Coordinate System Without Getting Left Behind"
1148:
776:
759:, you would be off by about 95 meters (not far enough west), and you'd be about 47 meters off near
163:
110:
494:- and gravimetric geoid model-based geometric reference frame and geopotential datum, potentially
573:
of 1866, then its latitude and longitude on that ellipsoid were defined and could be calculated.
301:
261:
511:
453:
752:
555:
281:
918:
862:
672:
567:
535:
515:
424:
341:
91:
21:
1126:
996:
985:
1009:
Encyclopaedia of scientific units, weights, and measures: their SI equivalences and origins
783:
241:
191:
117:
8:
649:
539:
153:
101:
897:
620:
These are the defining dimensions for NAD 27, but Clarke actually defined his 1866
543:
73:
43:
727:
1117:– a free utility for Microsoft Windows to convert between NAD 27 and NAD 83
1012:
787:
469:
173:
158:
1044:
1114:
969:
763:(not far enough north-northeast), whereas you would be much closer for points near
742:
417:
168:
1133:
1102:
480:
1078:
660:
381:
148:
122:
1108:
782:
In addition, NAD 83 is defined to remain constant over time for points on the
1142:
1120:
1032:
838:
816:
804:
800:
563:
495:
1095:
882:
North American Vertical Datum of 1988 (NAVD 88), at National Geodetic Survey
106:
959:
Van Zandt, Boundaries of the United States and the several states, p. 265
538:
at the junction of the transcontinental triangulation arc of 1899 on the
465:
63:
790:
are not on the North American Plate, so their divergence rate differs.
825:
To improve the National Spatial Reference System, NAD 83, along with
656:
461:
142:
68:
664:
621:
321:
138:
127:
764:
756:
559:
457:
201:
58:
35:
950:
Bulletin of the National Research Council, Issues 77-80, p. 230
668:
311:
271:
209:
663:
technology reached high precision and were made available for
908:
Shalowitz, USC&GS Field Engineers Bulletin, December 1938
842:
760:
490:
NAD 83, along with NAVD 88, is set to be replaced with a new
96:
919:"Where Theory Meets Practice: United States Standard Datum"
748:
736:
defined by the latitude and longitude of an initial point (
398:
291:
1111:- explanation of most recent adjustment of passive network
1105:- explanation of NAD 83(2011/MA11/PA11) epoch 2010.00
476:
based on slightly different assumptions and measurements.
28:, fundamental station for the North American Datum of 1927
491:
479:
Vertical measurements, based on distances above or below
745:") datum having no initial point or initial direction.
514:
called the United States Standard Datum, based on the
799:
Plate, while the MA11 and PA11 solutions are for the
501:
837:(GPS), and new gravimetric geoid model, potentially
648:
Because Earth deviates significantly from a perfect
793:
1045:"What is the Difference between WGS84 and NAD83?"
548:geographic center of the contiguous United States
331:
1140:
970:"Kansas and the geodetic datum of North America"
731:Datum Shift Between NAD 27 and NAD 83
643:
525:
1023:, Bull. Bur. Nat. Metrologie, 102 (1995) 5–14.
974:Transactions of the Kansas Academy of Science
770:
722:
425:
1033:NOAA's NAD 27 vs. NAD 83 converter
16:Reference frame for geodesy on the continent
1019:, p. 5, table 2.1, data from Giacomo, P.,
432:
418:
399:Spatial Reference System Identifier (SRID)
394:International Terrestrial Reference System
1096:NOAA-NGS-coordinates CORS-active network
933:United States Coast and Geodetic Survey,
898:New Datums: Replacing NAVD 88 and NAD 83
726:
20:
1011:, Springer-Verlag London Limited 2003,
893:
891:
889:
508:United States Coast and Geodetic Survey
1141:
1109:NOAA-NGS-coordinates passive network
858:North American Vertical Datum of 1988
827:North American Vertical Datum of 1988
485:North American Vertical Datum of 1988
886:
810:
723:Comparing NAD 27 to NAD 83
542:and the triangulation arc along the
875:
831:global navigation satellite systems
404:Universal Transverse Mercator (UTM)
366:European Terrestrial Ref. Sys. 1989
13:
738:Meades Ranch Triangulation Station
552:Meades Ranch Triangulation Station
502:First North American Datum of 1901
276:Ordnance Survey Great Britain 1936
242:Discrete Global Grid and Geocoding
133:Horizontal position representation
26:Meades Ranch Triangulation Station
14:
1170:
1089:
821:National Spatial Reference System
1123:– a web-based utility for NADCON
976:51 (1948) 117–124, www.jstor.org
794:Current implementation of NAD 83
777:slightly less flattened spheroid
483:(MHW), are calculated using the
192:Global Nav. Sat. Systems (GNSSs)
42:
1071:
1054:
1037:
1026:
1001:
990:
356:N. American Vertical Datum 1988
1154:Surveying of the United States
979:
962:
953:
944:
927:
922:Professional Surveyor Magazine
911:
902:
386:Internet link to a point 2010
316:Geodetic Reference System 1980
234:Quasi-Zenith Sat. Sys. (QZSS)
1:
868:
376:Chinese obfuscated datum 2002
917:Craig, Cindy (October 2013)
644:North American Datum of 1983
526:North American Datum of 1927
326:Geographic point coord. 1983
7:
851:
628:= 20,926,062 British feet,
286:Systema Koordinat 1942 goda
10:
1175:
939:Special Publication No. 70
814:
771:Comparing NAD 83 to WGS 84
550:. The datum declares the
474:geodetic reference systems
346:World Geodetic System 1984
935:"Triangulation in Kansas"
835:Global Positioning System
336:North American Datum 1983
306:South American Datum 1969
197:Global Pos. System (GPS)
164:Spatial reference system
1021:Du platine a la lumiere
456:now used to define the
841:. The new gravimetric
732:
556:Osborne County, Kansas
29:
1007:Cardarelli, Francois
863:World Geodetic System
730:
564:Waldo, Russell County
536:triangulation station
92:Geographical distance
24:
1132:26 June 2011 at the
833:(GNSS), such as the
784:North American Plate
694:(by definition)
687:(by definition)
592:(by definition)
585:(by definition)
446:North American Datum
266:Sea Level Datum 1929
118:Geodetic coordinates
1159:Surveying of Canada
1101:15 May 2013 at the
968:Walter H. Schoewe,
924:Frederick, Maryland
540:39th parallel north
510:adopted a national
296:European Datum 1950
254:Standards (history)
154:Reference ellipsoid
102:Figure of the Earth
733:
698:Inverse flattening
596:Inverse flattening
546:that was near the
544:98th meridian west
174:Vertical positions
30:
811:New Datum of 2022
788:San Andreas Fault
720:
719:
713:6,356,752.3141 m
702:
695:
688:
618:
617:
600:
593:
586:
470:land-use planning
442:
441:
390:
389:
169:Spatial relations
159:Satellite geodesy
114:
1166:
1083:
1082:
1075:
1069:
1068:
1066:
1058:
1052:
1051:
1049:
1041:
1035:
1030:
1024:
1005:
999:
994:
988:
983:
977:
966:
960:
957:
951:
948:
942:
931:
925:
915:
909:
906:
900:
895:
884:
879:
700:
693:
686:
678:
677:
598:
591:
584:
576:
575:
512:horizontal datum
454:horizontal datum
434:
427:
420:
258:
257:
237:
229:
221:
213:
205:
145:
104:
46:
32:
31:
1174:
1173:
1169:
1168:
1167:
1165:
1164:
1163:
1149:Geodetic datums
1139:
1138:
1134:Wayback Machine
1103:Wayback Machine
1092:
1087:
1086:
1077:
1076:
1072:
1064:
1060:
1059:
1055:
1047:
1043:
1042:
1038:
1031:
1027:
1006:
1002:
995:
991:
984:
980:
967:
963:
958:
954:
949:
945:
932:
928:
916:
912:
907:
903:
896:
887:
880:
876:
871:
854:
823:
815:Main articles:
813:
796:
773:
725:
699:
692:
685:
646:
597:
590:
583:
528:
504:
481:Mean High Water
438:
409:
408:
255:
247:
246:
235:
227:
219:
211:
203:
187:
179:
178:
137:
87:
79:
78:
54:
17:
12:
11:
5:
1172:
1162:
1161:
1156:
1151:
1137:
1136:
1124:
1118:
1112:
1106:
1091:
1090:External links
1088:
1085:
1084:
1070:
1053:
1036:
1025:
1000:
989:
978:
961:
952:
943:
926:
910:
901:
885:
873:
872:
870:
867:
866:
865:
860:
853:
850:
812:
809:
807:respectively.
795:
792:
772:
769:
724:
721:
718:
717:
716:298.257222101
714:
711:
708:
704:
703:
696:
691:Semiminor axis
689:
684:Semimajor axis
682:
661:remote sensing
645:
642:
616:
615:
614:294.978698214
612:
611:6,356,583.8 m
609:
608:6,378,206.4 m
606:
602:
601:
594:
589:Semiminor axis
587:
582:Semimajor axis
580:
527:
524:
503:
500:
440:
439:
437:
436:
429:
422:
414:
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407:
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149:Map projection
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123:Geodetic datum
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99:
94:
88:
85:
84:
81:
80:
77:
76:
71:
66:
61:
55:
52:
51:
48:
47:
39:
38:
15:
9:
6:
4:
3:
2:
1171:
1160:
1157:
1155:
1152:
1150:
1147:
1146:
1144:
1135:
1131:
1128:
1125:
1122:
1119:
1116:
1113:
1110:
1107:
1104:
1100:
1097:
1094:
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1080:
1074:
1063:
1057:
1046:
1040:
1034:
1029:
1022:
1018:
1017:1-85233-682-X
1014:
1010:
1004:
998:
993:
987:
982:
975:
971:
965:
956:
947:
940:
936:
930:
923:
920:
914:
905:
899:
894:
892:
890:
883:
878:
874:
864:
861:
859:
856:
855:
849:
846:
844:
840:
836:
832:
828:
822:
818:
817:Datum of 2022
808:
806:
805:Pacific Plate
802:
801:Mariana Plate
791:
789:
785:
780:
778:
768:
766:
762:
758:
754:
750:
746:
744:
739:
729:
715:
712:
709:
706:
705:
697:
690:
683:
680:
679:
676:
674:
670:
666:
662:
658:
653:
651:
641:
638:
633:
631:
627:
623:
613:
610:
607:
604:
603:
595:
588:
581:
578:
577:
574:
572:
569:
565:
561:
557:
553:
549:
545:
541:
537:
531:
523:
520:
517:
513:
509:
499:
497:
493:
488:
486:
482:
477:
475:
471:
467:
463:
459:
455:
451:
447:
435:
430:
428:
423:
421:
416:
415:
413:
412:
405:
402:
400:
397:
395:
392:
391:
385:
383:
380:
379:
375:
373:
370:
369:
365:
363:
360:
359:
355:
353:
350:
349:
345:
343:
340:
339:
335:
333:
330:
329:
325:
323:
320:
319:
315:
313:
310:
309:
305:
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299:
295:
293:
290:
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279:
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265:
263:
260:
259:
251:
250:
243:
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238:
232:
230:
224:
222:
216:
214:
210:BeiDou (BDS)
208:
206:
200:
198:
195:
193:
190:
189:
183:
182:
175:
172:
170:
167:
165:
162:
160:
157:
155:
152:
150:
147:
144:
140:
136:
134:
131:
129:
126:
124:
121:
119:
116:
112:
111:circumference
108:
103:
100:
98:
95:
93:
90:
89:
83:
82:
75:
72:
70:
67:
65:
62:
60:
57:
56:
50:
49:
45:
41:
40:
37:
34:
33:
27:
23:
19:
1073:
1056:
1039:
1028:
1020:
1008:
1003:
992:
981:
973:
964:
955:
946:
938:
929:
921:
913:
904:
877:
847:
824:
797:
781:
774:
747:
734:
710:6,378,137 m
707:GRS 80
701:(calculated)
659:geodesy and
654:
647:
634:
629:
625:
619:
605:Clarke 1866
599:(calculated)
532:
529:
506:In 1901 the
505:
489:
478:
449:
445:
443:
186:Technologies
141: /
53:Fundamentals
18:
673:WGS 84
669:GRS 80
487:(NAVD 88).
466:cartography
64:Geodynamics
1143:Categories
1121:nadcon.prl
869:References
839:in 2024-25
743:geocentric
681:Ellipsoid
579:Ellipsoid
753:topo map)
657:satellite
650:ellipsoid
571:Ellipsoid
519:Ellipsoid
462:surveying
452:) is the
143:Longitude
69:Geomatics
1130:Archived
1099:Archived
1079:"NA2011"
986:NGS data
852:See also
803:and the
665:civilian
622:spheroid
458:geodetic
322:ISO 6709
220:(Europe)
218:Galileo
204:(Russia)
202:GLONASS
139:Latitude
128:Geodesic
86:Concepts
765:Chicago
757:Seattle
560:azimuth
496:in 2025
382:Geo URI
352:NAVD 88
262:NGVD 29
236:(Japan)
228:(India)
212:(China)
74:History
59:Geodesy
36:Geodesy
1115:NADCON
1015:
941:(1921)
568:Clarke
516:Clarke
468:, and
372:GCJ-02
362:ETRS89
342:WGS 84
332:NAD 83
312:GRS 80
272:OSGB36
226:NAVIC
107:radius
1065:(PDF)
1048:(PDF)
997:Waldo
843:geoid
761:Miami
755:near
635:Most
302:SAD69
282:SK-42
97:Geoid
1013:ISBN
819:and
749:NOAA
637:USGS
444:The
292:ED50
109:and
655:As
624:as
554:in
492:GPS
450:NAD
1145::
972:,
937:,
888:^
767:.
498:.
464:,
1081:.
1067:.
1050:.
741:"
630:b
626:a
448:(
433:e
426:t
419:v
113:)
105:(
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
