# Glossary

The GDAL glossary contains terms and acronyms found throughout the GDAL documentation

Affine Transformation

  A geometric change that preserves points, straight lines, and ratios, including scaling, rotating, or translating.

API

  Application Programming Interface. A set of rules that lets different software programs communicate and share data or functions.

Arc

  A curved segment of a circle or other curve, often used in geographic data to represent smooth curved lines or boundaries between points.

Band

  A single layer of data values within a raster dataset. In a single-band raster, each pixel contains one value - such as elevation in a DEM. A multi-band raster contains multiple such layers; for example, satellite imagery may include three bands representing Red, Green, and Blue channels.

Band Algebra

  A method for performing mathematical operations on one or more raster bands to produce a new output band or raster. Band algebra involves applying expressions - such as addition, subtraction, multiplication, division, or more complex functions—on pixel values across bands.

  See also

  GDAL Band Algebra.

Block Cache

  A memory cache that stores recently accessed blocks of data to reduce disk reads and improve performance.

Boolean

  A data type representing one of two values: True or False, commonly used in logical operations and conditions.

Coordinate Epoch

  The date tied to spatial coordinates in a dynamic reference frame, used to account for positional changes over time (e.g., due to tectonic motion).

Credentials

  Information (such as a username and password or tokens) used to verify the identity of a user or system for authentication and access control.

CRS

  Coordinate Reference System. A system that maps spatial data coordinates to real-world locations, combining a coordinate system with a reference surface like a projection or ellipsoid.

curl

  A command-line tool and library for transferring data with URLs, supporting protocols such as HTTP, HTTPS, FTP, and more. Commonly used for testing and interacting with web services.

DEM

  Digital Elevation Model. A raster representation of the height of the earth's surface.

Driver

  A software component that enables reading, writing, and processing of specific raster or vector data formats.

DTM

  Digital Terrain Model. A raster representation of the bare ground surface of the earth, excluding natural and man-made objects such as vegetation and buildings.

Ellipsoid

  A model used to approximate the Earth's shape in coordinate systems.

Environment Variable

  A variable in the operating system that can influence the behavior of running processes or applications.

  See also

  Configuration options.

Escaped Character

  Refers to a character or sequence modified to prevent it from being interpreted as code or control instructions, allowing it to be treated as literal data.

Euclidean Distance

  A measure of the straight-line distance between two points in space.

EPSG

  European Petroleum Survey Group. A group of geospatial experts for the petroleum industry (1986–2005), now part of IOGP (International Association of Oil & Gas Producers). Known for creating the EPSG Geodetic Parameter Dataset, a widely used database of coordinate systems and geodetic parameters.

File Handle

  An identifier used by an operating system to manage and access an open file during a program's execution.

GEOS

  Geometry Engine - Open Source. GEOS is a C/C++ library for computational geometry with a focus on algorithms used in geographic information systems (GIS) software. GEOS started as a port of the Java Topology Suite (JTS).

  See also

  https://libgeos.org/

Gridding

  The process of converting scattered or irregularly spaced data points into a regular, structured grid format.

  See also

  GDAL Grid Tutorial.

Georeference

  Linking data to real-world geographic coordinates so a location can be accurately mapped.

Georeferencing

  See Georeference.

Geotransform

  A set of parameters that defines how to convert pixel locations in an image to real-world geographic coordinates.

  See also

  Geotransform Tutorial.

GNM

  Geographic Network Model. A GDAL abstraction for different existed network formats.

  See also

  Geographic Networks Data Model.

Interpolation

  A mathematical and statistical technique used to estimate unknown values between known values.

  See also

  GDAL Grid Tutorial.

Hypsometric

  The measurement and representation of land elevation (or terrain height) relative to sea level.

Library

  A collection of software routines, functions, or classes that can be used by programs to perform specific tasks without having to write code from scratch. Libraries help developers reuse code and simplify software development.

Linestring

  A geometric object consisting of a sequence of connected points forming a continuous line, commonly used to represent linear features such as roads or rivers in spatial data.

LRU Cache

  Least Recently Used Cache. A memory cache that stores a limited number of items, automatically discarding the least recently used entries to make space for new ones.

Moving Average

  A method that smooths data by averaging values over a sliding window of data points.

  See also

  GDAL Grid Tutorial.

Multithreading

  A programming technique where multiple threads are executed concurrently within a single process, allowing parallel execution of tasks to improve performance and responsiveness.

Normalizing

  The process of adjusting data values to a common scale. In raster analysis, normalizing is commonly used to scale pixel values to a defined range (such as 0 to 1) to facilitate comparison and visualization.

Nearest Neighbor

  A method that finds the closest data point(s) to a given point, often used for classification or estimation based on similarity.

OGC

  Open Geospatial Consortium. An international, non-profit organization that develops and promotes open standards for geospatial data and services.

  See also

  https://www.ogc.org/

OSR

  OGR Spatial Reference (OSR) - module that handles spatial reference systems and coordinate transformations.

  See also

  OGR Coordinate Reference Systems and Coordinate Transformation tutorial.

PAM

  Persistent Auxiliary Metadata. Metadata stored separately from the main raster data file, allowing additional information to persist without modifying the original file.

Raster

  A type of spatial data used with GIS, consisting of a regular grid of points spaced at a set distance (the resolution); often used to represent heights (DEM) or temperature data.

Raster Algebra

  See Band Algebra.

Resampling

  The process of changing the resolution or grid alignment of raster data by interpolating pixel values, used when scaling, reprojecting, or transforming images to maintain data quality.

RGB

  An acronym for Red, Green, and Blue - the three primary colors of light used in digital imaging.

Runtime

  The period during which a program or process is actively executing. It refers to the time from the start of a program's execution to its termination.

Search Ellipse

  Search window in gridding algorithms specified in the form of rotated ellipse.

  See also

  GDAL Grid Tutorial.

Search Window

  A defined area within which data is analyzed or searched, often used in spatial analysis or image processing.

  See also

  GDAL Grid Tutorial.

Shell

  A command-line interface used to interact with an operating system by typing commands.

Side-car Files

  Auxiliary files stored alongside a primary data file that contain metadata or additional information without altering the original file.

SRS

  Spatial Reference System. A system that defines how spatial coordinates map to real-world locations. Often used interchangeably with CRS, though CRS is the more precise term in modern geospatial standards.

SSL

  Secure Sockets Layer. A security protocol that encrypts data transmitted over the Internet to ensure privacy and data integrity between a client and a server.

stdout

  Standard output stream used by programs to display output data, typically shown on the console or terminal.

Swath

  A contiguous block or strip of raster data processed or read at one time.

Thread

  A sequence of executable instructions within a program that can run independently, often used to perform tasks concurrently for better performance.

Topology

  The study and representation of spatial relationships between geometric features, such as adjacency, connectivity, and containment, ensuring data integrity in GIS by defining how points, lines, and polygons share boundaries and connect.

User-Agent

  A string sent by a web browser or client identifying itself to a web server, often including information about the software, version, and operating system.

UTF8

  A character encoding that represents text using one to four bytes per character, and capable of encoding all Unicode characters. Also referred to a UTF-8.

VRT

  Virtual Raster Tile: A lightweight XML-based GDAL format that references multiple rasters or vectors to create a virtual mosaic without duplicating data.

  See also

  VRT -- GDAL Virtual Format and VRT -- OGR Virtual Format

VSI

  Virtual System Interface. An interface for accessing files and datasets in non-filesystem locations, such as in-memory files, zip files, and over network protocols.

  See also

  GDAL Virtual File Systems (compressed, network hosted, etc...): /vsimem, /vsizip, /vsitar, /vsicurl, ....

Warping

  The process of geometrically transforming raster data to align with a different coordinate system, projection, or spatial reference, often involving resampling of pixel values.

  See also

  gdalwarp.

WFS

  Web Feature Service, an OGC standard that allows users to access geospatial vector data over the web.

  See also

  WFS - OGC WFS service

WKT

  Well-Known Text. Text representation of geometries described in the Simple Features for SQL (SFSQL) specification.

WKT-CRS

  Well-Known Text for Coordinate Reference Systems. A text format that defines how to describe coordinate reference systems and transformations between them in a standardized way. See the OGC WKT-CRS standard.

WKB

  Well-Known Binary. Binary representation of geometries described in the Simple Features for SQL (SFSQL) specification.

WMS

  Web Map Service, an OGC standard that allows users to request and display georeferenced map images over the web.

  See also

  WMS -- Web Map Services

## Credits and Acknowledgments

Some definitions have been created with the help of the following resources.

- Introduction to Spatial Data and Using R as a GIS by Nick Bearman, licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International

- The Good Docs Project Glossary Initiative, by various contributors to the project, used under the following Terms of Use.

- The MapServer Glossary covered by the MapServer Licensing.