Struggling to understand some of those technical terms?
Check out our glossary below for an explanation of the most commonly used GIS and IT words.
Address Locator: A dataset that stores the address attributes, associated indexes and rules that define the process for translating non-spatial descriptions of places such as street addresses, into spatial data that can be displayed as features on a map.
Aerial Imagery: Photographs of the earth’s surface taken from an aircraft.
API: Acronym for Application Programming Interface. A set of interfaces, methods, protocols and tools that application developers use to build or customise a software program.
ArcGIS online (AGOL): A web-based system for making, sharing, finding, and using maps, map layers, and data services. ArcGIS Online is a third party service from ESRI.
Attribute: Information about a feature on the map. This is stored in an attribute table which is linked to the feature and can be accessed by either clicking on the feature or using an identify tool. For example, attributes of a river might include its name, length, and survey date.
Attribute Query: A request for records of features in a table based on their attribute values. For example selecting only a specific County: County = “Antrim”.
Attribute Table: A database or tabular file containing information about a set of geographic features, usually arranged so that each row represents a feature and each column represents one feature attribute.
Background Map: A map showing physical and natural features of the landscape. This map is commonly used for depicting background reference information, onto which other additional information can be overlaid.
Basemap: A map showing physical and natural features of the landscape. This map is commonly used for depicting background reference information, onto which other additional information can be overlaid.
Bookmark: A shortcut that saves the current map view, including extents, active layers, and styles for future use.
Cascading Style Sheets (CSS): A standard for defining the layout or presentation of an HTML document. Style information includes font size, background colour, text alignment and margins.
Cookies: A cookie is a file that is placed on your hard drive with your temporary internet files while you are visiting a website. Cookies are used to track how visitors use a particular internet web site.
Coordinates: A pair of values that represents the distance from an origin (0,0) along two axes, a horizontal axis (x), and a vertical axis (y). On a map, x,y coordinates are used to represent features at the location they are found on the earth’s spherical surface.
Coordinate System: A reference framework consisting of a set of points, lines, surfaces, and a set of rules used to define the positions of points in space in either 2 or 3 dimensions. In Northern Ireland we use the Irish Grid Coordinate system.
Data: Distinct pieces of factual information organised for analysis or used to reason or make decisions. Data is usually formatted in a special way, and exists in a variety of forms such as numbers or text on paper, as bits and bytes stored in electronic memory, or as facts stored in a person’s mind. Data can comprise maps, satellite images, publications and other geospatial data.
Dataset: A grouping of data by subject topic or type.
Digital Elevation Model (DEM): The representation of continuous elevation values over a topographic surface referenced to a common datum. DEM’s are typically used to represent terrain relief.
Digital Terrain Model (DTM): see Digital Elevation Model.
Easting: The distance east of the origin that a point in a coordinate system, measured in the systems units.
Elevation: The vertical distance of a point of object above or below a reference surface (usually mean sea level). Elevation generally refers to the vertical height of the land.
ESRI: A worldwide Geographic Information System (GIS) software company.
Extensible Markup Language: Developed by the W3C, a standardised general purpose markup language for designing text formats that facilitates the interchange of data between computer applications. XML is a set of rules for creating standard information formats using customised tags and sharing both the format and data across applications.
Feature: A representation of a real-world object on a map. An example would be a road, a lake, a school etc.
Gazetteer: A list of geographic place names and their coordinates.
Geographic Data: Information describing the location and attributes of features, including their shapes and representation. Geographic data is the composite of spatial data (A point, line or area on a map) and attribute data (Information about that point, line or area).
Geographic Information System (GIS): A computer system for capturing, storing, checking, integrating, manipulating, analysing and displaying data related to positions on the earth’s surface.
Geometry: The measures and properties of points, lines and surfaces. In a GIS, geometry is used to represent the spatial component of geographic features.
Geoportal: A web resource that provides access to a broad array of related resources and services.
Geospatial Information (Geo-info): Includes legal surveys, property cadastre, aerial photography, satellite imagery, aeronautical and nautical charts as well as various types of maps such as topographic maps, and geological, agriculture and forestry maps.
Geospatial Data: Geoinfo or geodata with explicit geographic positioning information included, such as a road network from a GIS, or a geo-referenced satellite image. Geospatial data may include attribute data that describes the features found in the dataset.
GIS: See Geographic Information System
Grid Reference: In cartography, a grid is any network of parallel and perpendicular lines superimposed on a map and used for reference. These grids are usually referred to by the map projection or coordinate system they represent, such as universal transverse Mercator grid.
HTML: Acronym for Hypertext Markup Language. A markup language used to create web pages for publication on the Internet. HTML is a system of tags that define the function of text, graphics, sound, and video within a document, and is now an Internet standard maintained by the World Wide Web Consortium.
HTTP: Acronym for Hypertext Transfer Protocol. This is the protocol maintained by the World Wide Web Consortium for communicating between servers and clients to exchange HTML documents across the internet.
HTTPS: Acronym for Hypertext Transfer Protocol (Secure). A variant of HTTP enhanced by a security mechanism.
Identify: A tool that, when applied to a feature (by clicking it), opens a popup showing that feature’s attributes.
iFrame: An iFrame or Inline Frame is a HTML structure that allows another HTML document to be inserted into an HTML page. The iFrame is set up as a window frame of a specified size that scrolls along with the rest of the page, but the iFrame’s content can itself be scrolled if it is larger than the iFrame window.
Image Service: An image service provides access to raster data through a web service.
INSPIRE Directive: The INSPIRE Directive, which is written into UK and EU law, aims to create a European Union (EU) spatial data infrastructure. This infrastructure is intended to enable the sharing of environmental spatial information among public sector organisations and better facilitate public access to spatial information across Europe. INSPIRE is based on the infrastructures for spatial information established and operated by the 27 Member States of the European Union including Spatial NI. The INSPIRE Directive compels Public Bodies holding environmental data in any of 34 spatial data themes to make that data discoverable and readily available for use by Government and by the Public.
IP address: Acronym for Internet Protocol address. A unique number such as 10.36.37.4 that identifies each computer on the internet.
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Large Scale: Generally a map scale that shows a small area on the ground at a high level of detail. For OSNI, this is usually referred to 1:2500 mapping scales and below.
Latitude: The angular distance, usually measured in degrees north or south of the equator.
Layer: The visual representation of a geographic dataset in any digital map environment. Conceptually, a layer is more or less equivalent to a legend item on a paper map. On a road map, for example, roads, national parks, political boundaries, and rivers might be considered different layers. Layers often consist of spatial data on a specific topic (i.e. lakes, rivers, streams etc.) that is managed by a specific business unit.
Legend: The description of the types of features included in a map, usually displayed in the map layout. Legends often use graphics of symbols or examples of features from the map with a written description of what each symbol or graphic represents.
LIDAR: Acronym for Light Detection and Ranging. A remote sensing technique that uses lasers to measure distances to reflective surfaces.
Longitude: The angular distance, usually expressed in degrees, minutes and seconds of a location on the earth’s surface east or west of the Greenwich prime meridian.
Map Extent: The limit of the geographic area shown on a map. In a web map, the map extent can be changed by panning and zooming.
Map Service: Provides map images or map data over the internet via a web address URL. It is possible to display, navigate, zoom in and out, pan, and overlay the map data. The data is held on a server and a view of this data is displayed on the client such as a web browser or application.
Map Scale: The scale on a map expressed as a ratio indicating how much a given area has been reduced. For example, a paper map with a map scale of 1:24,000 means every 1 inch on the map is equivalent to 24,000 inches on the Earth’s surface. A small-scale map (i.e. 1:250,000) can show large amounts of area without much detail. While a large-scale map (1:1,200) can only show small area but lots of details. “Large scale” maps have relatively large objects, “small scale” maps reflect relatively small objects.
Map Viewer: The Spatial NI Map Viewer allows users to interact with geographic data using a variety of navigation and query tools.
Metadata: Metadata is a set of data that describes and gives information about the data. It is structured information that explains a dataset giving the reader more background as to how the information was gathered, how often the data is updated, and contact details for the data owner etc. The metadata standard used on Spatial NI is UK GEMINI Version 2.2. For more information please visit the Association of Geographic Information (AGI) website.
Min/Max Scale: The smallest and largest scales at which a layer is visible on the map. For Spatial NI these are 1:500 and 1:2,000,000.
Northern Ireland GI Strategy: A strategy which aims to make Northern Ireland a spatially enabled society by 2019. Government will use GI (geographic information) as a decision making tool. Businesses will use GI to increase efficiency and the public will be actively using GI on a daily basis.
NIMA: Acronym for Northern Ireland Mapping Agreement is a centrally funded agreement which allows Land & Property Services Geographic Information (GI) to be used by all Northern Ireland Civil Service Departments, Agencies, Non Departmental Public Bodies, and Local Councils.
Northing: The distance north of the origin that a point in a coordinate system, measured in the systems units.
Open Geospatial Consortium (OGC): An internal consortium of companies, government agencies and universities participating in a process to develop publicly available geospatial and location based services. For more information, visit the OGC website.
Orthophotograph (Ortho): Orthophotography (ortho) is enhanced aerial photography. Orthophotographs are scale-accurate images that offer a detailed bird’s-eye view of the landscape. The images show natural and man-made details on the earth’s surface. Any distortions caused by the earth’s surface or aircraft movement have been removed to make sure that the images are accurate. This process is called orthorectification. Photographs are taken in optimal weather conditions to provide the best possible images.
Overlay: A spatial operation in which two or more maps or layers registered to a common coordinate system are superimposed for the purpose of observing relationships between features that occupy the same geographic space.
Overview map: A generalised, smaller-scale map that shows the limits of another map’s extent along with its surrounding area.
Pan: To shift a map image relative to the display window without changing the viewing scale.
PDF: Acronym for Portable Document Format. A proprietary file format from Adobe that creates lightweight text-based formatted files for distribution.
Pixel: The smallest unit of information in an image or raster map.
Pixel size: The dimensions on the ground of a single pixel in a raster, measured in map units.
Polygon: On a map, a closed shape defined by a connected sequence of x,y coordinate pairs, where the first and last coordinate pair are the same and all other pairs are unique.
Postcode: A series of letters and numbers in a specific format used by Royal Mail to simplify the delivery of mail.
Privacy Statement: A statement that outlines how your data will be treated in a careful and secure manner while using the Spatial NI portal.
Projected Coordinate System: A projected coordinate system is defined on a flat, two-dimensional surface. Locations are identified by x,y coordinates on a grid. One specifies its horizontal position and the other its vertical position. The two values are called the x-coordinate and y-coordinate. Using this notation, the coordinates at the origin are x = 0 and y = 0.
Projection: A method by which the curved surface of the earth is portrayed on a flat surface. Every map projection distorts distance, area, shape, direction or a combination of them all.
Query: A request to select features or records from a database. A query is often written as a statement or logical expression.
Raster: A spatial data model that defines space as an array of equally sized cells arranged in rows and columns, and composed of single or multiple bands. Each cell contains an attribute value and location coordinates. Unlike a vector structure, which stores coordinates explicitly, raster coordinates are contained in the ordering of the matrix. Groups of cells that share the same value represent the same type of geographic feature.
REST: Acronym for Representational State Transfer. An architecture for exchanging information between peers in a decentralised, distributed environment. REST allows programs on different computers to communicate independently of an operating system by sending a HTTP request to a URL and getting back data in a format e.g. XML. REST is used in web services.
Scale: To change the size of an object while maintaining its shape. Most graphics software, particularly vector-based packages, allow you to scale objects freely. In the GIS world, scale refers to the reduction of area to show portions of the Earth’s surface on a map.
Seamline: A polygon that defines the mosaic boundary of a raster dataset used in an image service. OSNI use seamlines to define how orthophotos are constructed.
Service: A persistent software process that provides data or computing resources for client applications.
Shapefile: A shapefile is a digital vector storage format for storing geometric location and associated attribute information. Shapefiles spatially describe geometries: points, polylines, and polygons. These, for example, could represent water wells, rivers, and lakes, respectively.
Spatial data: Information about the locations and shapes of geographic features and the relationships between them, usually stored as coordinates and topology.
Spatial (Geospatial) Data Infrastructure (SDI): The relevant base collection of technologies, policies and institutional arrangements that facilitate the availability of and access to spatial data. A spatial data infrastructure provides a basis for spatial data discovery, evaluation and application for users and suppliers within all levels of government, the commercial sector, the non-profit sector, academia and citizens in general.
Spatial Query: A statement or logical expression that selects geographic features based on location or spatial relationship. For example, a spatial query might find which points are contained within a polygon or set of polygons, find features within a specified distance of a feature, or find features that are adjacent to each other.
Theme: A set of related geographic features such as streets, parcels, or rivers, along with their attributes. All features in a theme share the same coordinate system, are located within a common geographic extent, and have the same attributes. High level classification of data (i.e. hydrography) comprised of a multitude of spatial data layers (i.e., lakes, rivers, streams etc.).
URL: A uniform resource locator, abbreviated as URL (also known as web address, particularly when used with HTTP), is a specific character string that constitutes a reference to a resource. In most web browsers, the URL of a web page is displayed on top inside an address bar.
Vector: A coordinate-based data model that represents geographic features as points, lines, and polygons. Each point feature is represented as a single coordinate pair, while line and polygon features are represented as ordered lists of vertices. Attributes are associated with each vector feature, as opposed to a raster data model, which associates attributes with grid cells.
Web browser: An application that allows users to access and view Web pages on their computer screens. Web browsers enable users to view HTML documents on the World Wide Web.
Web Feature Service (WFS): Feature services serve feature data over the internet often allowing you to edit the features.
Web Map Service (WMS): Provides map images or map data over the internet via a web address url. It is possible to display, navigate, zoom in and out, pan, and overlay the map data. The data is held on a server and a view of this data is displayed on the client such as a web browser or application.
WMTS: Acronym for Web Mapping Tile Service. The WMTS tile resource represents a single cached file which is a fragment of a map representation of a layer in the content of WMTS specification.
X,Y Coordinates: See Coordinates
XML: Acronym for Extensible Markup Language. Developed by the W3C, a standardised general purpose markup language for designing text formats that facilitates the interchange of data between computer applications. XML is a set of rules for creating standard information formats using customized tags and sharing both the format and the data across applications.
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Z Coordinates: The value for a given surface location. In an elevation or terrain model, the z-value represents elevation.
Zoom: To display a larger or smaller region of an on-screen map or image.