GIS Glossary/Q

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GIS Glossary

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QQ plot

A scatter chart in which the quantiles of two distributions are plotted against each other.

quad sheet

A rectangular map bounded by lines of latitude and longitude, often a map sheet in either the 7.5-minute or 15-minute series published by the U.S. Geological Survey. Quadrangles are also called topo sheets.


A rectangular map bounded by lines of latitude and longitude, often a map sheet in either the 7.5-minute or 15-minute series published by the U.S. Geological Survey. Quadrangles are also called topo sheets.


In a rectangular coordinate system, any of the quarters formed by the central intersection of x and y axes that divide a plane into four equal parts.


In spatial sampling, one of a set of identically-sized areas, often rectangular, within which the members of a population are counted. The size, number, and location of quadrats within a study area are chosen by the sampler. Population counts in each quadrat are compared to determine distribution patterns.

quadrat analysis

Comparison of the statistically expected and actual counts of objects within spatial sampling areas (quadrats) to test for distribution patterns such as randomness and clustering.


A method for encoding raster data that reduces storage requirements and improves access speeds by storing values only for homogeneous regions rather than for every pixel. The raster is recursively subdivided into quadrants until all regions are homogeneous or until some specified level has been reached.

qualitative data

Data classified or shown by category, rather than by amount or rank, such as soil by type or animals by species.

quality assurance

A process used to verify the quality of a product after its production.

Quality Beta

In ArcGIS Survey Analyst, when used together, the F test and W test are called the B method of testing, for which a power can be defined. This power is the Quality Beta, and can be defined as follows: the probability that the null hypothesis is accepted while, in fact, it is false, is equal to 1-b.

quality control

A process used during production of a product to ensure its quality.


In a data distribution, a value representing a class break, where classes contain approximately equal numbers of observations. The p-th quantile, where p is between 0 and 1, is that value that has a proportion p of the data below the value. For theoretical distributions, the p-th quantile is the value that has p probability below the value.

quantile classification

A data classification method that distributes a set of values into groups that contain an equal number of values.

quantitative data

Data grouped or shown by measurements of number or amount, such as population per unit area.

quantitative geography

The application of mathematical and statistical concepts and methods to the study of geography.


A request to select features or records from a database. A query is often written as a statement or logical expression.

query expression

A type of expression that evaluates to a Boolean (true or false) value, that is typically used to select those rows in a table in which the expression evaluates to true. Query expressions are generally part of a SQL statement.

query interface

A client may request a reference to a different interface on an object by calling the QueryInterface method of the IUnknown interface.

query language

A language for storing, retrieving, and editing data in a database.

query server

A private ArcIMS virtual server that works with an image server to support query functions. When a viewer requests an identify or find operation, the query server returns the related geographic or tabular data. It can be built against shapefiles, ArcSDE layers, and joined external tables.

query table

A table containing results from a query.

Query Web Service

A SOAP ArcWeb service for determining the characteristics and features for a specified location. With Query Web Service, users can specify which attributes are available to query, set the level of geography for the query, and generate a list of attributes or field names and their descriptions for a point, area, envelope, or dataset.