# Shared Flashcard Set

## Details

Spatial Stats
Quiz 2
24
Environmental Studies
02/12/2015

Term
 Covariance
Definition
 A statistical measure of the linear relationship between two variables. Covariance measures the degree to which two variables move together relative to their individual variabilities.
Term
 Distribution
Definition
 The frequency or amount at which a thing or things occur within a given domain.
Term
 Histogram
Definition
 A graph showing the distribution of values in a set of data. Individual values are displayed along a horizontal axis, and the frequency of their occurrence is displayed along a vertical axis.
Term
 Interpolation
Definition
 The estimation of surface values at unsampled points based on known surface values of surrounding points. Interpolation can be used to estimate elevation, rainfall, temperature, chemical dispersion, or other spatially based phenomena.
Term
 Isotropy
Definition
 A property of a natural process or data where spatial dependence (autocorrelation) changes only with the distance between two locations—direction is unimportant. Anisotropy occurs where spatial dependence (autocorrelation) changes with both the distance and the direction between two locations.
Term
 Mean
Definition
 The average for a set of values, computed as the sum of all values divided by the number of values in the set.
Term
 Mean Center
Definition
 The location of a single x,y coordinate value that represents the average x-coordinate value and the average y-coordinate value of all features in a study area.
Term
 Median
Definition
 The middle value of a set of values when they are ordered by rank. When there are two middle values (if the set has an even number of elements), the median is the mean of these two values.
Term
 Normal Distribution
Definition
 A frequency distribution of a dataset in which the distribution of values can be graphically represented as a symmetrical bell curve. Normal distributions are typically characterized by a clustering of values near the mean, with few values departing radically from the mean. There are as many values on the left side of the curve as on the right, so the mean and median values for the distribution are the same.
Term
 Outlier
Definition
 An unusual or extreme data value in a dataset. In data analysis, outliers can potentially have a strong effect on results and must be analyzed carefully to determine if they represent valid or erroneous data.
Term
 Polynomial
Definition
 A mathematical function that is the sum of at least two terms and has the form: [image] where n is a non-negative integer and where each value {an, ..., a0} is a constant. Each component of the polynomial equation is referred to as a term. The order of the polynomial refers to the exponent, or degree, of the leading term.
Term
 QQ Plot
Definition
 A scatter plot in which the quantiles of two distributions are plotted against each other. The most common type of QQ plot is the normal QQ plot.
Term
 Semivariogram
Definition
 A function of the distance separating two locations that is used to quantify dependence. It is calculated as half of the squared difference between two data values at two locations. The semivariogram generally increases with distance before becoming flat and is described by nugget, sill, and range parameters. If the data is stationary, then the semivariogram represents the spatial autocorrelation structure of the data.
Term
 Spatial Autocorrelation
Definition
 A measure of the degree to which data values depend on their spatial locations.
Term
 Spatial Stats
Definition
 The field of study concerning statistical methods that use space and spatial relationships (such as distance and/or other spatial characteristics of data) directly in their mathematical computations. Spatial statistics are used for a variety of different types of analyses, including point pattern analysis, surface modeling and prediction, spatial regression, and more.
Term
 Standard Deviation
Definition
 A statistical measure of the spread of values from their mean, calculated as the square root of the sum of the squared deviations from the mean value, divided by the number of elements minus one. The standard deviation for a distribution is the square root of the variance.
Term
 Stationarity
Definition
 In geostatistics, a property of a spatial process in which the covariance between the values of any two points depends only on the distance between them.
Term
 Thiessen polygon
Definition
 Polygons generated from a set of sample points. Each Thiessen polygon defines an area of influence around its sample point so that any location inside the polygon is closer to that point than to any of the other sample points.
Term
 Trend
Definition
 In a spatial model, non-random variation in the value of a variable that can be described by a mathematical function such as a polynomial.
Term
 Voronoi Map
Definition
 A partition of space into areas, or polygons, that surround a set of geometric objects (usually points) such that all locations within a polygon are closer to the object it surrounds than to any other object in the set. The value of each polygon is determined by the values of the objects in neighboring polygons, so a Voronoi map can be used to investigate local variation. Voronoi maps are also often used to delineate areas of influence around geographic features. Voronoi maps are named for the Ukrainian mathematician Georgy Fedoseevich Voronoi (1868-1908).
Term
 Ratio Scale Data
Definition
 A constant interval and true zero point
Term
 Interval Scale Data
Definition
 A constant iinterval but with NO true zero point
Term
 Ordinal Scale Data
Definition
 No constant interval
Term
 Nominal Scale Data
Definition
 Quality rather than quantity is measured
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