GIS Glossary - Clearview Geographic

By Alex Morse 09/25/2023

Welcome to our GIS Glossary! This page serves as a resource to explain some of GIS, cartography, remote sensing, and geographic terms. Below you’ll find these terms defined in an alphabetical arrangement. If you want to add or request that we add something to our GIS glossary email our web development team at webmaster@clearviewgeographic.com

Accuracy

The closeness or nearness of the measurements to the true or actual value of the quantity being measured. In GIS, accuracy is often determined through comparison with an authoritative source and is usually represented as a percentile.

Aerial Photography

The practice of taking photographs from elevated platforms such as aircraft, drones, or satellites. These photos can be georeferenced and used in GIS for analysis or as a visual layer.

Alphanumeric

A set of characters containing both letters and numbers. Often used in GIS to label or identify features, like a parcel ID that might include both letters and numbers (e.g., “A1B-223”).

Arc

A line segment defined by its geometry (start and end points) and its attributes. In GIS, arcs are often used to represent linear features such as roads or rivers.

Area of Interest (AOI)

A defined geographic space that is the subject of particular study or project in GIS.

Areal Unit

A specific geographic area or region that is the subject of spatial analysis, such as a census tract or a ZIP code area.

Aspect

The direction in which a surface slope faces, usually described in terms of cardinal directions (N, S, E, W). Aspect is often used in studies of terrain, soil erosion, or vegetation patterns.

Attribute

Descriptive or qualitative information associated with a spatial feature. For example, the attributes of a city point feature could include the city name, population, and average income.

Attribute Table

A table in a GIS that stores data describing the attributes of spatial features. Each row represents a unique spatial feature, and each column represents a different attribute.

Azimuth

The angular measurement of an object’s direction in degrees, usually measured from true north or magnetic north. Used in navigation and in specifying the orientation of lines or features on a map.

Axis

A reference line in Cartesian coordinate systems (like the x-axis and y-axis) used for determining the coordinates of a point in two-dimensional or three-dimensional space.

Base Map

A map displaying background reference information such as landforms, roads, landmarks, and political boundaries, onto which other thematic information can be layered.

Bathymetry

The study and mapping of underwater topography, including the depths and shapes of oceanic and other water bodies’ floors.

Bearing

The horizontal angle between the direction of an object and a reference direction, usually north. Used to describe the direction of one point from another, with a reference axis usually being north.

Boolean Operations

In GIS, these are operations that involve combining two or more spatial datasets to create a new output dataset based on conditions like “AND,” “OR,” and “NOT.”

Buffer

A zone around a map feature measured in units of distance or time. A buffer is useful for proximity analysis; for example, identifying all homes within 300 feet of a river.

Byte

A unit of digital information storage, often used to describe the size of data files or the amount of disk storage space. GIS files can be quite large and may require significant storage space.

Bilinear Interpolation

A resampling method used in image processing to estimate pixel values. This method takes the weighted average of the four nearest pixels to derive a value for a new pixel.

Bitmap

A type of graphic composed of pixels in a grid. Each pixel can be a different color or shade. Bitmaps are often used for digital elevation models and satellite images.

Bivariate Analysis

Analysis involving the relationship between two different sets of variables.

Boundary

The outer limit or edge of a spatial feature, usually represented by lines (vector) or pixels (raster).

Breaklines

Linear features that represent a change in the surface form and are used in the creation of a TIN (Triangulated Irregular Network) to model the surface in 3D.

Building Footprint

The outline of a building at ground level. Building footprints are commonly used in GIS to represent the location and shape of buildings on a map.

Cartography

The practice of creating maps, including the design principles, techniques, and interpretation involved.

Cartouche

An ornamental frame around the title, legend, or other information on a map.

Cadastral Map

A map that shows land ownership and property boundaries.

Choropleth Map

A thematic map where geographical areas are shaded in proportion to the variable being measured.

Coordinate System

A system for defining the location of points in space using coordinates, such as latitude and longitude.

Contour Line

A line on a map connecting points of equal elevation.

Clip

The GIS process of removing portions of one layer based on the boundary of another layer.

Conflation

The alignment and merging of two different map layers to form a single, integrated layer.

Coverage

A type of spatial data representation that includes points, lines, and polygons.

Cursor

In the context of databases, it’s a control structure for traversing records in a database.

Census Data

Statistical data collected from a population, often used in demographic analyses in GIS.

Datum

A reference surface against which spatial coordinates are measured.

Discrete Data

Spatial data divided into distinct units, such as points, lines, and polygons.

Digitizing

The process of converting analog information into a digital format, often involving the use of a digitizing tablet or on-screen manual tracing to capture spatial data.

Data Integrity

The accuracy and consistency of a data set.

Database Management System

A software system used for the creation and management of databases, commonly used in GIS for spatial databases.

Draping

The process of overlaying one spatial data layer onto another. Typically, an image or map is “draped” over a topographic surface.

Data Dictionary

A document that outlines the structure, type, and restrictions of data within a database.

Density Mapping

Creating a map that shows the concentration of a particular variable in a given area.

Drawing Exchange Format

A CAD data file format, used for storing two and three-dimensional design data and metadata.

Digital Elevation Model

A digital model or 3D representation of a terrain’s surface, often used for topographical mapping.

Digital Line Graph

A digital vector representation of cartographic information, designed for use in GIS systems.

Dissolve

The process of removing boundaries between adjacent polygons that share the same value for a specified attribute.

Dithering

A technique used to create the illusion of more colors or shades than actually exist in the data, by arranging pixels of available colors in a specific pattern.

Delineation

The process of identifying and marking boundaries or defining features on a map.

Distance Decay

A geographical term which describes the effect of distance on interactions between places.

Ellipsoid

A three-dimensional shape that is slightly flattened at the poles and bulging at the equator, used as a simplified model of the Earth’s shape.

Ecliptic

The apparent path of the Sun as seen from the Earth, useful in solar radiation studies in GIS.

Euclidean Distance

The straight-line distance between two points in a plane, often used in spatial analysis.

Enumeration District

A geographical area defined for the purpose of taking a census.

Edge Matching

The process of ensuring that features on the edge of one map layer match or align perfectly with corresponding features on an adjacent map layer.

Export

In GIS context, the act of saving spatial data into a different format that can be used in other applications.

Exponential Smoothing

A statistical method used to forecast spatial patterns or trends by assigning exponentially decreasing weights to past observations.

Feature

A spatial object or entity, which can be point, line, or polygon, representing real-world phenomena.

Field

A category of information, often represented as a column in a database, that is attached to spatial features.

File Format

The structure in which data is stored, read, and manipulated in a GIS system.

Filtering

The process of selecting a subset of data based on certain criteria, such as value thresholds or geographic boundaries.

Flow Direction

The direction in which water, people, goods, etc., move from one point to another, often represented as vectors in GIS.

Friction Surface

A concept in GIS modeling that assigns a cost value to movement across a landscape, often based on terrain difficulty, land use, or other variables.

Full Extent

The complete spatial range visible in a GIS interface, displaying all available data layers.

Fractal

A complex structure made up of simpler copies of itself at any scale, often used to model natural phenomena.

Fuzzy Logic

A mathematical approach that allows for the inclusion of vagueness and uncertainty in analytical reasoning.

Geocoding

The process of converting addresses or other textual locational descriptors into geographic coordinates that can be displayed as features on a map.

Geofence

A virtual boundary around a real-world geographic area, often used in mobile applications to trigger certain actions when a device enters or exits the area.

Geodatabase

A database designed to store, query, and manipulate geographic information and spatial data.

Geoid

The shape that the surface of the Earth’s oceans would take under the influence of Earth’s gravity and rotation alone.

Geographic Coordinates

A system of latitude and longitude used to define the spatial location of features on the Earth’s surface.

Georeferencing

The process of aligning spatial data layers with real-world coordinates by using control points.

Geospatial

Pertaining to the geographic location and characteristics of natural or constructed features and boundaries on, above, or below the Earth’s surface.

Grid

A regular pattern of lines, either in a plane (2D) or in space (3D), used to represent spatial relationships.

Heatmap

A graphical representation of data where individual values are represented as colors, often used to show the density of points in a given area.

Hillshade

A grayscale 3D representation of a surface, with the sun’s relative position taken into account for shading the image.

Homogeneous

A term used to describe an area that contains a single type of feature or attribute.

Hydraulic Modeling

The simulation of water flow in channels and pipelines, often carried out with GIS software.

Hyperlink

A link from a hypertext document to another location, activated by clicking on a highlighted word or image within the document.

Hydrology

The study of the distribution, movement, and properties of water in the Earth’s atmosphere and surface, often represented in GIS through hydrological models.

Hypsography

The study of the distribution of elevations on the surface of the Earth, commonly represented through contour lines in GIS.

Imagery

Photographic data collected from satellites or high-flying aircraft, used in mapping and various types of analysis.

Interpolation

A mathematical method for estimating values of a continuous variable at locations where no data exist, based on known values at other locations.

Isoline

A line on a map connecting points that have the same value for a given variable, such as temperature or elevation.

Identifier

A unique label or code used to reference a particular record in a dataset.

Inset Map

A smaller map set within the larger main map, used to display additional information at a different scale.

Intersection

The geometric representation of shared space between two or more spatial datasets, often used in spatial analysis to identify areas of overlap.

Join

The process of linking two different sets of data based on a common attribute or field.

JPEG (Joint Photographic Experts Group)

A widely-used image file format that allows for compressed storage of raster images.

Junction

A point where two or more lines meet or intersect, commonly used in network analysis.

Justification

The alignment of text within a bounding box or designated area on a map.

Kriging

A method of interpolation that uses statistical models to predict values in unmeasured locations based on observed data points.

Kernel Density

A method of smoothing point data to create a continuous surface, often used in heatmaps.

Keyhole Markup Language (KML)

A markup language used for expressing geographic data in an XML format.

Knot

A point on a curve or surface where a parameter changes value, commonly used in spline interpolation.

Knot Vector

In spline interpolation, a sequence that defines the positions and weights of knots in the spline curve.

Land Cover

The physical material at the surface of the Earth, which can include grass, asphalt, trees, bare ground, water, etc.

Land Use

The human activity occurring on a piece of land, like residential, industrial, or agricultural use.

Label

Text or other markers used to identify features on a map.

Layer

In GIS, a set of geographic features that are represented with the same symbology and are usually one aspect of a map, such as roads or rivers.

Legend

The key to the symbols used on a map, explaining what each symbol represents.

Line

In GIS, a one-dimensional object that has length but no area, representing linear features such as roads, rivers, and utility lines.

Lineage

The history of changes to a dataset, including edits, projections, and transformations.

Loess

A form of statistical smoothing used in data analysis and graphing.

Linear Referencing

A method for storing geographic locations using relative positions along a pre-defined linear feature, rather than x, y coordinates.

Locator Map

A smaller map set in the corner of a larger map, used to show the area covered by the main map in a broader geographic context.

Map Scale

The ratio between a distance on a map and the corresponding distance on the ground, often expressed as a fraction or ratio.

Map Series

A set of maps that cover an area in several sheets, where each sheet shows a different portion of the area.

Mosaic

The process or result of merging multiple images or raster datasets into a single, continuous image.

Map Algebra

A set of cell-by-cell mathematical operations used to manipulate raster data layers.

Metadata

Information that describes the content, quality, and other characteristics of data.

Multi-Resolution

The capability of a raster or image to be displayed at different levels of detail.

Multi-Spectral Imagery

Imagery that captures data at specific frequencies across the electromagnetic spectrum, including frequencies beyond human vision.

Nautical Mile

A unit of distance equal to one minute of latitude along any meridian, commonly used in marine navigation.

Navigable

Refers to water bodies that are deep and wide enough to be used for transportation.

Normal Distribution

A probability distribution often used in statistical analyses, where data clusters around a mean value.

Null Value

A value that signifies missing or undefined data in a dataset.

Neighborhood Analysis

A type of spatial analysis that looks at the relationship between a feature and its surrounding features within a specific radius.

Network Analysis

The process of evaluating interconnected features, such as roads or rivers, to find the most efficient routes or assess connectivity.

Node

A single point that serves as an end or intersection of linear features, such as the end points of a line or where two lines meet.

Normalization

The process of adjusting values measured on different scales to a common scale, often used in map comparisons and statistical analyses.

Orthophoto

A photograph that has been geometrically corrected such that the scale is uniform and can be used to measure true distances.

Overlay Analysis

The process of layering multiple maps or layers to merge information into a single map.

Overlay

The process of superimposing layers of data to perform complex spatial analyses.

Origin

The point of intersection of the x, y, and sometimes z axes in a Cartesian coordinate system.

Object-Oriented

A data model in which geometric features are represented as objects with both spatial and attribute information.

Outlier

A data point that is significantly different from other data points in a data set.

Planimetric

Refers to maps that display only the horizontal positions of features; elevation information is not included.

Precision

The level of measurement granularity, usually defined by the number of decimal places in coordinates.

Polygon

In GIS, a shape with multiple sides representing an area, such as a park, lake, or city boundary.

Proximity Analysis

The process of identifying the spatial relationship between features based on their closeness to each other.

Pixel

The smallest unit in a raster image, representing a single point in the grid and storing a value that represents a characteristic of that point, such as elevation or color.

Quadrangle

A map or chart that represents a four-sided area, usually a section delineated by latitude and longitude lines.

Quantile

A value or set of values that divide a dataset into equal intervals, often used in data classification.

Quaternion

A mathematical concept used in 3D rotations, useful in some geospatial applications.

Quincunx

A pattern of five points forming a cross, often used in sampling methods in geography and remote sensing.

Query

A request for data or information from a database table or combination of tables. Queries are a fundamental part of GIS to filter and analyze data.

Quantitative Data

Numerical information that can be measured and analyzed, such as temperature or elevation.

Quickbird

A high-resolution commercial earth observation satellite, often used in GIS for acquiring imagery.

Raster

A grid-based data format that represents geographic space as an array of equally sized square cells. Each cell holds a single attribute value and location coordinates.

Remote Sensing

The science of acquiring information about an object or area from a distance, often using satellite or aerial imagery.

Region

A set of contiguous polygons usually grouped together because they share a common characteristic.

Relief

The variations in elevation and slope in a particular geographic area.

Resolution

The level of detail that a map displays, typically determined by the size of the smallest feature that can be represented.

Route Analysis

The use of GIS technology to determine the most efficient pathways for point-to-point travel, factoring in variables such as speed limits, and types of roads.

Scale

The ratio of distance on a map to the corresponding distance on the ground. For example, a 1:10,000 scale map means 1 unit on the map equals 10,000 units on the ground.

Spatial Analysis

A method in GIS for examining the locations, attributes, and relationships of features in spatial data through overlay and other techniques.

Symbology

The use of symbols to represent geographic features on a map. For instance, a blue line might symbolize a river.

Surveying

The scientific method of determining positions of points and the distances and angles between them. Often used in the construction of maps.

Shapefile

A commonly used vector data format for storing spatial data and attribute information.

Spline

A smooth curve used to interpolate between known points in both 2D and 3D spatial analyses.

Spatial Join

The operation of merging two datasets based on a shared spatial characteristic.

Thematic Map

A map that focuses on a specific theme or subject area, such as population density or land use.

Topography

The physical characteristics of a landscape, including both natural and artificial features like rivers, mountains, and roads.

Topological Model

A data model in GIS that stores the spatial relationships between features. This can include adjacency, connectivity, and containment.

Topological Error

Errors in a vector dataset that break the rules of topology, such as overlapping polygons or intersecting lines.

Transect

A straight line or narrow section across a natural feature or population area, along which observations are made.

Triangulated Irregular Network (TIN)

A vector-based representation of the spatial distribution of a scalar quantity, used for the digital representation of the surface.

Uncertainty

The degree to which the data in a GIS database is uncertain, often arising due to errors in data collection, processing, or interpretation.

Universal Transverse Mercator (UTM)

A coordinate system that divides the Earth into 60 zones, each being 6 degrees longitude wide and extending from 80 degrees south latitude to 84 degrees north latitude.

Unprojected Data

Spatial data that has not been fitted to a map projection, thus it represents a spheroid or ellipsoid earth model.

User Interface

The medium through which a GIS user interacts with the software or hardware, typically consisting of menus, toolbars, and a map display.

Uncertainty

A measure of the reliability or precision of data, usually expressed in terms of variance, standard error, or confidence intervals.

Union

An operation that combines the geometries of two layers into a single layer, retaining all unique areas.

Utility Mapping

The mapping of underground utilities and services within a given area for the purpose of construction, development, and repair.

Uplift

The vertical elevation of Earth’s crust, usually due to tectonic forces, which can be studied using spatial techniques.

Vector Data

A type of spatial data represented by points, lines, and polygons. It is used in GIS to represent features like cities, roads, and lakes.

Vertex

A single point in a geometry, such as a corner of a polygon or an endpoint of a line.

Viewshed

The area visible from a certain point, taking into account the topography of the terrain. Viewshed analysis is commonly used in fields like urban planning, forestry, and environmental science.

Virtual Reality Modeling Language (VRML)

A standard file format for representing 3D interactive vector graphics, often used in GIS for complex simulations.

Voronoi Diagram

A partitioning of a plane with n points into convex polygons such that each polygon contains exactly one generating point and every point in a given polygon is closer to its generating point than to any other.

Vulnerability Assessment

The identification of risks and vulnerabilities in a geographic area, often using GIS to map disaster-prone locations.

Watershed

A land area that channels rainfall and snowmelt to creeks, streams, and rivers, eventually flowing to outflow points such as reservoirs, bays, and the ocean.

Waypoint

A specific point in physical space that someone can use to establish themselves in relation to other points, often used for navigational purposes.

Web Mapping

The process of using web technologies to display, manipulate, and analyze geographic information online. Often uses web-based GIS software and tools.

Web Map Service (WMS)

An online map service that enables users to build interactive maps by stacking multiple map layers from various web sources.

WebGIS

A GIS application or service that is accessed and operated through a web browser.

Weighted Overlay

A technique used to combine multiple spatial data layers by applying a common scale of values for analysis.

WGS84

The World Geodetic System 1984, a geodetic reference system that serves as the foundation for precise GPS coordinates.

X-coordinate

The horizontal value in a two-dimensional coordinate system.

XML (eXtensible Markup Language)

A general-purpose specification for creating custom markup languages. It is used for both the definition of the content structure and the description of data within GIS systems, although it is not a GIS-specific term.

X-ray Diffraction

A technique occasionally used in soil analysis in geography to identify mineral structures.

XYZ Format

A simple text file format that stores coordinate data as tuples of X, Y, and Z values, often used in 3D applications.

Yield

In agricultural geography, the amount of a particular crop produced per unit of land.

Y-coordinate

The vertical value in a two-dimensional coordinate system.

Y-intercept

The point where a line intersects the Y-axis in a Cartesian coordinate system.

Younger Dryas

A paleoclimate event often studied in historical geography for its sudden and drastic climatic changes.

Youth Bulge

A demographic pattern often analyzed using GIS, where a large percentage of a population is composed of young people.

Z-coordinate

In a three-dimensional coordinate system, the Z-coordinate represents the elevation or depth of a point.

Zenith

The point in the sky directly above an observer, important in various types of remote sensing.

Zero Population Growth

A demographic balance where the number of births equals the number of deaths, often analyzed spatially to understand population trends.

Zonal Statistics

Statistical operations performed on values of a raster within the zones of another dataset. Often used to analyze the spatial correlation between two different variables.

Zoom

The act of changing the scale of a map to view more or less detail. You can zoom in to see greater detail or zoom out to see a larger geographic area.

Zoogeography

The study of the geographical distribution of animals, often involving GIS to map distributions and identify patterns.

This concludes ClearGeo’s A to Z GIS glossary. We invite both active GIS professionals and those new to the field to use this resource as a quick reference tool.

Common Acronyms utilized in GIS industry

Below is a list of 100 common acronyms and their associated meanings.

API – Application Programming Interface
ASCII – American Standard Code for Information Interchange
AVHRR – Advanced Very High-Resolution Radiometer
CAD – Computer-Aided Design
CERES – Clouds and the Earth’s Radiant Energy System
CGA – Cartographic and Geospatial Analysis
COGO – Coordinate Geometry
CRS – Coordinate Reference System
CSV – Comma-Separated Values
DBMS – Database Management System
DEM – Digital Elevation Model
DGN – Design File Format
DMS – Degrees, Minutes, Seconds
DOP – Dilution of Precision
DPI – Dots Per Inch
DRG – Digital Raster Graphic
DSM – Digital Surface Model
DTED – Digital Terrain Elevation Data
DTM – Digital Terrain Model
DXF – Drawing Exchange Format
ECEF – Earth-Centered, Earth-Fixed
EDM – Electronic Distance Measurement
EPSG – European Petroleum Survey Group
ERDAS – Earth Resources Data Analysis System
ESRI – Environmental Systems Research Institute
ETM – Enhanced Thematic Mapper
FTP – File Transfer Protocol
GCP – Ground Control Point
GDAL – Geospatial Data Abstraction Library
GDB – Geodatabase
GEBCO – General Bathymetric Chart of the Oceans
GEOINT – Geospatial Intelligence
GeoJSON – Geospatial JavaScript Object Notation
GEOTIFF – Georeferenced Tagged Image File Format
GIS – Geographic Information System
GISc – Geographic Information Science
GNSS – Global Navigation Satellite System
GOES – Geostationary Operational Environmental Satellites
GPS – Global Positioning System
GRASS – Geographic Resources Analysis Support System
GUI – Graphical User Interface
GVP – Global Volcanism Program
HTTP – HyperText Transfer Protocol
HTTPS – HyperText Transfer Protocol Secure
IDW – Inverse Distance Weighting
IERS – International Earth Rotation and Reference Systems Service
IGS – International GNSS Service
IMU – Inertial Measurement Unit
INSAR – Interferometric Synthetic Aperture Radar
ITRF – International Terrestrial Reference Frame
JSON – JavaScript Object Notation
KML – Keyhole Markup Language
LANDSAT – Land Satellite
LBS – Location-Based Services
LiDAR – Light Detection and Ranging
LOD – Level of Detail
MODIS – Moderate Resolution Imaging Spectroradiometer
MOLA – Mars Orbiter Laser Altimeter
MSS – Multispectral Scanner
NAD27 – North American Datum of 1927
NAD83 – North American Datum of 1983
NAP – North American Profile
NATRF – North American Terrestrial Reference Frame
NED – National Elevation Dataset
NEMA – National Marine Electronics Association
NGA – National Geospatial-Intelligence Agency
NHD – National Hydrography Dataset
NMEA – National Marine Electronics Association
NOAA – National Oceanic and Atmospheric Administration
OGC – Open Geospatial Consortium
OGDI – Open Geographic Datastore Interface
OGR – OpenGIS Simple Features Reference Implementation
OSM – OpenStreetMap
PAN – Panchromatic
PCA – Principal Component Analysis
PDOP – Positional Dilution of Precision
PGDB – Personal Geodatabase
PLS – Public Land Survey System
PMF – Published Map File
QA/QC – Quality Assurance/Quality Control
RADAR – Radio Detection and Ranging
REST – Representational State Transfer
RGB – Red, Green, Blue
RINEX – Receiver Independent Exchange Format
RTK – Real-Time Kinematic
SAR – Synthetic Aperture Radar
SDTS – Spatial Data Transfer Standard
SEMA – Spherical Elementary Magnetic Anomaly
SHP – Shapefile
SIT – Self-Identifying Tile
SLD – Styled Layer Descriptor
SQL – Structured Query Language
SRID – Spatial Reference ID
SSURGO – Soil Survey Geographic Database
SVG – Scalable Vector Graphics
TIGER – Topologically Integrated Geographic Encoding and Referencing
TIN – Triangulated Irregular Network
UML – Unified Modeling Language
USGS – United States Geological Survey
VRT – Virtual Raster Table