COMPARE WITH
This is tool that we use in the glossary for juxtaposition. We also have tools like SEE and SEE ALSO but without question if a term comes with the direction COMPARE WITH it has at some point in its existent cause a certain amount of confusion and or trouble in its usage and implementation in the world of mapping sciences. One my favorite pairs is accuracy and precision because it has such a rich history of confusion at some many different scales of use.
accuracy 1. n., The difference (unsigned) between a specified value of a particular quantity and a value that has been accepted as correct for that quantity. When this difference is known and has a sign, it may be called a correction or an error, depending on the viewpoint of the user. When the difference is known only very approximately, it is usually referred to merely as high accuracy if small and low accuracy if large, without stating numerical values. 2. n., A measure of the closeness of a set of values, measured or calculated, to the true value. Also called outer accuracy or external accuracy by some European writers. Accuracy is sharply distinguished, in English, from precision, which is a measure of the closeness of the measurements to each other. So a very precise set of measurements can be much less accurate than a different set which is more accurate but less precise. For example, some early geodesists using a few poor measurements were able to find values of the Earth's flattening quite close to the value now accepted as correct, while later geodesists using more precise data obtained values considerably farther from the present value. The history of measurements of the speed of light provides another example of many, presumably very precise, measurements gave quite erroneous values for the speed. Several different kinds of measure are in use. (a) The square root of the average value of the sum of squares of the differences between the values in a set and the corresponding correct or standard values. This is the most common measure and is usually referred to as the accuracy of the set of values. It is also referred to as the outer accuracy or external accuracy if the precision is referred to as the inner accuracy. (This latter terminology is rare in American usage.) If {xi} is the set of values (measured of calculated) and if s is + √ [ Ʃ (xi ‑ xio)²]/M then s is a measure of the accuracy if {xio} is a set of correct or standard values and M = I (the number of values in the set). It is the precision if xio = x, the average value of the {xio} and if M = I ‑ 1. (b) The average of the sum of the absolute values of the differences between the measured or calculated values and the correct or standard values. (c) The reciprocal of the s defined in (a). Accuracy cannot be calculated solely from the measured or calculated values. A standard (correct) value or set of such values must be used for comparison. The standard may be (a) an exact value, such as the sum of the three angles of a plane triangle; (b) the value of a conventional unit, such as the length of the International Meter, defined from the speed of light in a vacuum; (c) a value determined by refined methods and deemed sufficiently near the correct value that it can be used as such: e.g., the adjusted elevation of a permanent bench mark or the graticule of a map projection. COMPARE WITH precision. 3. n., The standard deviation. This is a measure of precision. It should never be used as a measure of accuracy. 4. n., The root-mean-square error. This is approximately the same as the standard deviation and, like it, should not be used as a measure of accuracy. 5. When the set {xi} consists of calculated numbers (e.g. those in a mathematical table), the term accuracy may mean (a) the number of significant digits in the numbers; (b) the magnitude of the least significant digit; or (c) the number of correct places in the numbers.
precision 1. n., In statistics, a measure of the tendency of a set of random numbers to cluster about a number determined by the set. The usual measure is either the standard deviation (with respect to the average), or the reciprocal of this quantity. Precision is not the same as accuracy; the latter is a measure of the tendency of a set of numbers to cluster about some number determined not by the set but specified in some more or less arbitrary manner independent of the set. COMPARE WITH accuracy. 2. n., In physics, in metrology and in the art of measuring in general, a measure of the quality of the method by which measurements are made. In this sense, precision differs from accuracy in that the latter relates the quality of the results of the measurements, not the quality of the method used. Precision applies not only to the fidelity with which required operations are preformed, but by custom has been applied to methods and instruments employed in obtaining results of a high order of precision. Precision is exemplified by the number of decimal places to which a computation is carried out and a result stated. In a general way, the accuracy of a result should determine the precision with which it is expressed. Two different kinds of precision are sometimes distinguished: repeatability and reproducibility. Repeatability is then a measure of the amount by which measurements made by one instrument differ from each other. Reproducibility is a measure of the amount by which measurements made by different instruments differ from each other. 3. n., The quantity 1/(σsqrt(2)), in which σ is the standard deviation of the random variable involved. Also called a precision index or index of precision. SEE ALSO modulus of precision. 4. adj., SEE precise.
Here are a few more to think about:
abut 1. v., To touch, as contiguous estates, along a border or with a projecting part. 2. v., Cause to abut ; support something by abutting. 3. adj.,Terminating or touching with an end. Two parcels adjoin if they have a common side; they abut if they have a common end. COMPARE WITH adjoining.
adjoining 1. adj., Touching, as distinguished from being merely close to or adjacent. adjoining and abutting are at present often used as if they were synonymous. However, it is recommended that the old distinction be retained where possible. Two parcels adjoin if they have a common side; they abut if they have a common end. COMPARE WITH abut. 2. adj., Close to. This usage is improper but, fortunately, rare.
«»
calculation, floating-point n., Calculation in which each quantity used is represented by two numbers: a coefficient and an exponent (e.g. 3.9528‑2 and 1.01101‑3 also written 3.9528*10-2 and 1.01101*10-3 respectively); the rules of arithmetic are applied separately to coefficient and exponent. Quantities are added or subtracted by first multiplying the coefficients by suitable powers of 10 to make the exponents the same and then doing the calculations on the coefficients. Quantities are multiplied or divided by multiplying or dividing the coefficients and at the same time adding or subtracting their exponents. COMPARE WITH calculation, fixed-point.
calculation, fixed-point n., Calculation in which each quantity used is represented by a single number (e.g., 395.28 and 10110.1) and the calculation is done according to the usual rules of arithmetic. In fixed-point calculations, the decimal point is not moved. Contrasted with floating-point calculation, in which each quantity is represented by two numbers and the decimal point is moved so that it immediately precedes or follows the most significant digit. COMPARE WITH calculation, floating-point.
«»
calendar year n., The interval of time containing an integral number of days, the exact number being set by law or custom but usually 365 days plus or minus a few days, and designated as a year in a particular calendar. A calendar year always contains an integral number of days; an astronomical year never does. The round of seasons follows the astronomical calendar. The number of days in a calendar year is therefore changed from time to time according to some rule set by law, custom, or religion, so that the average length of the calendar year and the astronomical year will remain approximately equal. SEE ALSO calendar COMPARE WITH year, tropical.
year, tropical 1. n., The interval of time during which the Sun's mean longitude, referred to the mean equinox of date, increases by 360°. Also called an astronomical year, equinoctial year, natural year and solar year. The tropical year is the basis for the conventional calendar year used in chronology and civil reckoning. It is, to a close approximation, the average length of time required for the Sun to pass from vernal equinox to vernal equinox. COMPARE WITH calendar year. 2. n., The average interval between two successive passages of the Sun through the vernal equinox.
year, astronomical 1. The period of time between two successive passages of the Sun through the same right ascension (the Besselian year) or longitude (the tropical year). The length of the day and the length of the astronomical year are incommensurable. 2. SEE year, tropical.
«»
camera, metric n., A camera constructed so that its photographic characteristics remain, do not change from photograph to photograph, and the image is as little distorted as possible (i.e., a camera whose calibration constants remain constant over long periods of time and which gives minimal distortion). Also called a precise camera. Metric cameras are essential for most photogrammetric projects. Non-metric cameras require, at best, frequent recalibration. COMPARE WITH camera, non-metric.
camera, non-metric 1. n., A camera not designed specifically for use in photogrammetry. 2. n., A camera which has unknown or very poorly known internal geometry including focal length, principal point and lens distortion properties. COMPARE WITH camera, metric.
«»
horizon, apparent 1. n., That irregular line, on the Earth's surface, which bounds the regions within which points are visible to an observer or detector. (Points outside that same line therefore are not visible from the point of observation.) Also called the horizon, geographic horizon, local horizon, topocentric horizon, visible horizon and visual horizon. It is the line where the visible surface of the Earth appears to meet the sky. When the apparent horizon is formed by the surface of a body of water, it is sometimes used as a reference in observing vertical angles. SEE ALSO horizon, dip of the. 2. n., The apparent horizon is farther from the observer than the geometric horizon except where a temperature inversion causes the rays of light (or other radiation) to bend upwards instead of downwards as is normal. Its location depends not only on the topography and on the point of observation but also on the refractivity of the air. COMPARE WITH horizon, geometric.
horizon, geometric 1. That line, on the Earth's surface, at which straight lines from the point of observation are tangent to the Earth's surface. Also called geometrical horizon and true horizon, although the latter term is also used for the plane of the horizon, apparent horizon, and celestial horizon. The term surface in this definition must be interpreted loosely; the surface proper may be hidden by buildings, trees, etc. The geometric horizon is usually closer to the observer than the apparent horizon; the latter is defined by the concave paths of rays from the surface to the observer. 2. That curve, on an ellipsoid representing the Earth, at which lines through the assumed point of observation are tangent to the ellipsoid. Points within the geometric horizon are visible from the point of observation; points outside the geometric horizon are not. 3. The intersection (line) of the celestial sphere with a plane tangent to the Earth's surface and passing through the eye of the observer. Earth's surface actually means, here, a sphere or ellipsoid representing the Earth's surface; tangent to the Earth's surface means parallel to a plane tangent to the representing sphere or ellipsoid. 4. SEE horizon, celestial. 5. A plane through the center of the Earth and parallel to the plane of the apparent horizon (a plane fitted in some suitable manner to the apparent horizon). COMPARE WITH horizon, apparent.
moonrise (moonset) 1. That position of the Moon, at rising (setting), in which the apparent upper limb of the Moon is on the astronomical horizon. 2. That position of the Moon, at rising (setting) in which the true zenith distance, referred to the center of the Earth, of the central point of the disk is 90° 34'+ a‑p; 34' is the conventional value of horizontal refraction, a is the length of the Moon's semidiameter and p is the horizontal parallax. COMPARE WITH sunrise (sunset).
sunrise (sunset) 1. The apparent rising (setting) of the Sun above the horizon. 2. The time at which the apparent upper limb of the Sun is on the astronomical horizon when the Sun is rising (setting); i.e., when the true zenith distance, referred to the center of the Earth, is 90° 50', based on adopted values of 34' for horizontal refraction and 16' for the Sun's semidiameter. COMPARE WITH moonrise (moonset). SEE ALSO twilight.
The importance of understanding which measuring stick we are using when we write down our thoughts and conduct our research. We may understand what we mean but others may not; this is why we define our terms and measures in all research writing.
In this blog we will post terms and themes of related terms and their definitions that come from the The Glossary of Mapping Sciences with commentary. In the hope that by discussing the meaning of words we come to deeper understanding and more meaningful usage.