North American Datum of 1983
Because Earth deviates significantly from a perfect ellipsoid, 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.
As satellite geodesy and remote sensing technology reached high precision and were made available for civilian 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 GRS 80 ellipsoid was developed for best approximating the earth as a whole, and it became the foundation for the North American Datum of 1983. Though generally GRS 80 and its close relative WGS 84 are 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.
| Ellipsoid | Semimajor axis† | Semiminor axis†† | Inverse flattening†† |
| GRS 80 | 6,378,137 m | 6,356,752.3141 m | 298.257222101 |
†By definition. ††Calculated.
Read more about this topic: North American Datum
Famous quotes containing the words north american, north, american and/or datum:
“The compulsion to do good is an innate American trait. Only North Americans seem to believe that they always should, may, and actually can choose somebody with whom to share their blessings. Ultimately this attitude leads to bombing people into the acceptance of gifts.”
—Ivan Illich (b. 1926)
“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)
“It seems that American patriotism measures itself against an outcast group. The right Americans are the right Americans because they’re not like the wrong Americans, who are not really Americans.”
—Eric J. Hobsbawm (b. 1917)
“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)