North American Datum of 1927
The North American Datum of 1927 (NAD27) is based on the Clarke Ellipsoid of 1866; it was created by manual surveying of the entire continent. The geodetic "center" of NAD27 is a base station at Meades Ranch in Kansas.
| Ellipsoid | Semimajor axis† | Semiminor axis† | Inverse flattening†† |
| Clarke 1866 | 6,378,206.4 m | 6,356,583.8 m | 294.978698214 |
†By definition. ††Calculated.
These are the defining dimensions for NAD27, but Clarke actually defined his 1866 spheroid as a = 20,926,062 British feet, b = 20,855,121 British feet. The conversion to meters uses Clarke's 1865 inch-meter ratio of 39.370432. In a practical sense, the length of a foot or meter at the time could not be benchmarked to better than about 0.02 mm, so the meter equivalents used now can be considered exact to well beyond the uncertainties in the lengths and conversion values of the time.
Read more about this topic: North American Datum
Famous quotes containing the words north, american and/or datum:
“Biography is a very definite region bounded on the north by history, on the south by fiction, on the east by obituary, and on the west by tedium.”
—Philip Guedalla (1889–1944)
“What the vast majority of American children needs is to stop being pampered, stop being indulged, stop being chauffeured, stop being catered to. In the final analysis it is not what you do for your children but what you have taught them to do for themselves that will make them successful human beings.”
—Ann Landers (b. 1918)
“Language fails not because thought fails, but because no verbal symbols can do justice to the fullness and richness of thought. If we are to continue talking about “data” in any other sense than as reflective distinctions, the original datum is always such a qualitative whole.”
—John Dewey (1859–1952)