Glossary

Attribute Table – A table of non-spatial attributes associated with features or cells in a spatial data set, in ArcView either a Feature Theme or Grid Theme. Referred to in ArcView as a theme table. Arc-WofE's weights and probability calculations are performed on values read from a theme's attribute table.

Binary – Describes an evidential theme with two classes. One class typically denotes a pattern, and the other class denotes areas off the pattern. Areas of missing data are considered separately from either class. Refer to Weights of Evidence Method, Binary Evidential Themes.

Buffer – A polygon enclosing an area within specified distance from a point, line or polygon. In Arc-WofE, buffering is performed using Spatial Analyst so the output is always a Grid (raster). The buffering function generates 1 or more buffers of equal distance from the input features. Input can be either vector or raster data.

Categorical Weights – Refers to weights calculated for each class in an evidential theme. In Arc-WofE, describes one of the tables of weights that can be created using the 'Calculate Theme Weights...' function, distinguishing it from tables of cumulative weights. Refer to Cumulative Weights; Calculating Theme Weights... Categorical; Calculating Response Theme... Output Weights Table.

Class The value or range of values identified as a separate attribute in an evidential theme. 'Class value' is sometimes used in the documentation. Class field refers to the field in an evidential theme's attribute table that contains the classes you want to analyze. Class descriptors are strings or labels that describe the class, which will most often be identified by an integer.

Conditional Independence An assumption of conditional independence is made in the weights of evidence model. Refer to Check Conditional Independence...; Overall Test of Conditional Independence; Weights of Evidence Method, Conditional Independence.

Cumulative Weights Refers to weights calculated for cumulative number of points and areas for classes in ordered data. Cumulative weights calculated from either highest to lowest (descending), or lowest to highest (ascending) class, can be calculated for a single evidential theme in the 'Calculate Theme Weights...' function. Calculating cumulative weights can be useful in reducing noise from variation that occurs in categorical weights, making it easier to determine the optimum cut-off points for generalization of data. Refer to Categorical Weights; Ordered Data Type; Calculating Theme Weights... Cumulative.

Free Data Type Describes data that have a categorical or nominal measurement scale, for example, the class values on a geological map. Refer to Ordered Data Type; Calculating Theme Weights...

Evidential Theme A spatial data set used as evidence for prediction of point objects (e.g. mineral occurrences). Arc-WofE is able to use polygon features themes (shape files or coverages) or integer grid themes (Grid format) as evidential themes. (Floating point grids are not suitable for direct input to Arc-WofE because attribute tables are not associated with floating point grids.) Also referred to as an evidence map, predictor map. Refer to Weights of Evidence Method, Evidential Theme.

Feature Theme ArcView's representation of a vector data set. Each feature theme contains a single feature type. Arc-WofE expects its training point theme to be a point feature theme. Evidential themes can be polygon feature themes.

Grid Theme ArcView's representation of ESRI's raster Grid format. An evidential theme in Arc-WofE can be an integer grid theme. Arc-WofE's study area grid theme is required to be a grid theme, and response themes created by Arc-WofE are automatically integer grid themes. Refer to ArcView's On-line Help Topic:What is a grid theme?

Generalization In the context of Arc-WofE, the process of simplifying the thematic information of an evidential theme by classifying (grouping) existing classes in the theme's attribute table to fewer classes in a new field. Refer to Generalizing an Evidential Theme...

Ordered Data Type Describes data that use an ordered measurement scale. Refer to Free Data Type.

Response Theme – An output map that expresses the probability that a unit area contains a point, estimated by combining the weights of the predictor variable (evidential themes). The theme is based on a unique conditions grid and its attribute table. Refer to Weights of Evidence Method, Response theme and Map Combination.

Study Area Grid Theme – A grid theme used to define the geographic extent of your study area. All cells in the grid theme that contain a value are included in the study area;all cells containing 'No Data' are excluded. Refer to Set Analysis Parameters... Study Area Grid Theme; Weights of Evidence Method, Study Area Theme.

Unit Area – Also called unit cell, this is the unit, measured in square kilometres, in which areas are measured for weights calculations. The unit area is not related to the analysis (or output) cell size. Refer to Weights of Evidence Method, Unit Cell; Setting Analysis Parameters... Defining Area Units.

Unique Conditions Grid/Table – An integer grid formed from the combination of two or more evidential themes (input themes), in which the class values represent uniquely-occurring combinations of the classes of the input themes. Each class value is therefore a "unique condition", or unique combination of the input themes. The attribute table associated with the unique conditions grid (unique conditions table) has one record per unique condition class, and contains fields with posterior probability and other calculated variables. Refer to Weights of Evidence Method, Map Combination; ArcView On-Line Help Topic: Combine (Grid); Calculating Response Theme...

Training Point Theme – Point feature theme in which each point is used as a training point in the calculation of weights. In an exploration model, each training point is a known mineral occurrence or deposit. Refer to Weights of Evidence Method, Training Point theme.

Weights Table – A table created by Arc-WofE in one of two formats, that reports the weights, contrast and associated measure for each class in an evidential theme... (1) The weights tables produced for a single evidential theme using the 'Calculate Theme Weights...' function provides a more complete picture of the data set. (2) The weights table created for a set of evidential themes contains weights which are used in turn to calculate posterior probabilities, logits and measures of uncertainty. An associated variances table is also calculated.

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