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Ordnance Survey - Glossary: mapping terminology and acronyms
Category: Electronics and Engineering > mapping
Date & country: 24/09/2007, UK
Words: 415


Platform Independent
A term usually applied to a piece of software that can operate on many different hardware platforms e.g. PC, Unix, Mac, VAX etc.

Plot
The provision of an extract of the data as a single plot or print on paper or similar medium.

Point
A zero-dimensional spatial abstraction of an object represented by a coordinate pair.

Point and Line Data Structure.
A form of vector data structure designed for map production in which all map features are designated as points or lines or text. Point and line data does not carry the topological relationships between features.

Point Feature
A zero-dimensional spatial abstraction of an object with its position defined by a coordinate pair. Points may also be represented by symbols which may have attributes such as orientation and size.

Polygon
Polygons are representations of areas. A polygon is defined as a closed line or perimter which completely encloses a contiguous space and is made up of one or more links. At least one node occurs on the perimeter of a polygon where the bounding link completes the enclosure of the area. There may be many nodes connecting the bounding links of a polygon. Links may be shared between polygons. Polygons ma wholly contain other polygons; or be contained within other polygons.

Polygon Boundary
The link or links which enclose a polygon, projected into the horizontal plane.

Polygon Point
See Representative Point.

Polyline
A line made up of a sequence of line segments.

Portal
A web-site or service that offers a window into a broad array of resources and services. A portal also allows the provider and/or user to customise the content of the web-site to meet individual needs.

Positional Accuracy
The degree to which the coordinates define a point's true position in the world, directly related to the spheroid and/or projection on which the coordinates system is based.

Positional Quality
Gives an indication of the positional accuracy of the location coordinates in ADDRESS-POINT.

Postal Address
A series of instructions used by Royal Mail to sort and distribute mail to a delivery office for delivery to the intended recipient. It contains only those address elements that are necessary to identify one delivery point from another to assist Royal Mail in the delivery of mail. There may be many delivery points within an individual building structure as shown in Land-Line data.

Postal Address File
Created when all the sparately held information was assembled and stored on a Royal Mail central computer system. PAF® now contains the postal addresses and postcodes of approximately 25 million delivery points including approximately 170 000 large users.

Postcode
The units by which the delivery of post is managed by Royal Mail. There are four components to the code: The 'Area', i.e. 'SO', the 'District', i.e. '16', the 'Sector', i.e. '4' and 'Unit', i.e. 'GU'. A so-called 'Unit Postcode', the smallest postal unit.

Pre-Build
Depiction of detail before construction.

Protocol
A formally agreed standard for communication between computers.

Proxy Server
A server that acts as an intermediary between a client and the server the client wants to access. It is the proxy server that makes the request to the server of interest and passes back the response to the client.

Query
The process of selecting features in a database. Can be acheived through a query language directly on the data or, in a GIS, by interactively selecting features.

RAD
See Rapid Application Development.

Rapid Application Development
An approach to software development based on close collaboration with users and a continuous iterative delivery of software.

Rasterisation
The process that converts vector data, which is a series of points, lines and polygons into raster data which is a series of cells with a discrete value.

RDBMS
See Relational Database Management System.

Receiver Independent Exchange
Exchange format for GPS observations. Provision is made for pseudorange, carrier phase and Doppler observations.

Record
A set of related data fields grouped for processing.

Rectangular Coordinates
Also known as x-y coordinates and as eastings and northings. These are two-dimensional coordinates which measure the position of any point relative to an arbitrary origin on a plane surface e.g. A map projection, a digitising table or a VDU screen.

Red, Green and Blue
The primary colours of light perceived by the eye.

Reformed Mapping
A method of improving the accuracy of overhaul mapping. It consists of a partial resurvey based on air triangulation and completion by fit and trace methods of pockets old detail to match the new.

Relational Database
One which stores data in rows and tables e.g. Oracle, MS Access.

Relative Accuracy
Relative accuracy compares the distance between features measured on the ground to the corresponding information contained in the map data. When measuring between data points represented on the map it is worth noting that some distortion may occur due to the materials and process used to produce the map.

Relative Coordinates
A coordinate pair or triplet measured relative to another point in the coordinate system in which it lies, rather than from the origin. (see also absolute coordinates).

Remote Holdings
The situation where the supplier holds and manages the customer's data.

Remote Sensing
The process of obtaining information about an object whilst separated by some distance from the subject. Practically, this is a term used to describe the process of using sensors mounted on satellites to observe the Earth's geology, surface and atmosphere.

Representative Point
A point within a polygon that can be used to carry the attributes of the whole polygon e.g. owner or land use type. Also called area seed, peg point, point label, polygon point, polygon seed. Representative points are not included in OS MasterMap data.

Resampling
An increase or reduction in the number of pixels in an image, reqired to change its resolution without altering its size. See also down-sampling and interpolation.

Resolution
A measure of the ability to detect quantities. High resolution implies a high degree of discrimination but has no implication as to accuracy e.g. In a collection of data in which the coordinates are rounded to the nearest metre, resolution will be 1 metre, but the accuracy may be +/-5 metres or worse.

Resurvey
The complete survey of detail based directly on National Grid control (OSGB36). It may be completed wholly on the ground or by a combination of aerial and ground survey methods.

RGB
See Red, Green and Blue.

RINEX
See Receiver Independent Exchange.

Road Centreline
An implied and imaginary line depicting the centre of a road carriageway (represented by FC0098 in Land-Line in NTF or G8010098 in Land-Line in DXF). They are not specifically surveyed or precisely positioned within the data. They are digitised to fall between curb lines, but will nit necessarily fall equidistantly between them.

Rotation
Movement of a vector through an angle.

Router
In a message switching system, the portion of a node or exchange that examines incoming messages, interprets the address information and determines which of the outgoing links can be used. Usually a computer program that chooses messages from incoming buffers and places them into outgoing message queues.

RS
See Remote Sensing.

Rubber Sheeting
A process which adjusts the relative positions of features within a dataset in a non-linear or non-uniform way. It is used to transform the coordinates of maps with different scales, orientation or coordinate systems.

Sampling
The process of converting analogue data into digital data by taking a series of samples or readings at equal time intervals.

Scanning
Capturing an image using an optical input device that uses light sensing equipment. The image is translated into a digital signal that can be manipulated by optical character recognition software or graphics software.

Schema
A description of a feature's attributes or, more specifically, the specific attribution model for a feature in terms of primitive data types and constraints on these types.

Segment
A link or line defined by two consecutive coordinates in a line string.

Server
A program that runs on a networked computer that responds to client programs running on other networked computers.

Service Level Agreement
See Collective Agreement.

Shapefiles
A simplistic geospatial data structure in which objects are stored individually with no explicit information about the relationships between those objects.

Single Precision
Refers to a level of coordinate accuracy based on the number of significant digits that can be stored for each coordinate. Single-precision numbers store up to 7 significant digits for each coordinate.

SLA
See Service Level Agreement.

Small Scale
The opposite of large scale and relates to a map that covers a wide area. Called small scale because features that appear on the map will look to be smaller in size than those on a larger scale map.

Snapping
An operation or process whereby whereby the computer will move a point or line slightly so that it corresponds to a nearby point or closest point on a nearby line.

Soft Clipping
All line features that fall across a query area are supplied complete. For areas, the area feature itself will refer to all the lines that bound it. However, only those lines partly or entirely within the query area are supplied. OS MasterMap data will only be supplied unclipped.

Spaghetti Data
Vector data composed of line segments which are not topologically structured or organised into objects and which may not even be geometrically clean. Spaghetti data can be useful however if all that is required is a visual image or a plot of a map.

Spatial Analysis
A family of analytical techniques associated with the study of spatial objects, their location, geometry and attributes. The analysis can simply be visual, by association and location, or mathematical.

Spatial Data
Another term used to describe Geospatial Data.

Spatial Entity
See Feature.

Spatial Query
The process of selecting features based on location or spatial relationship e.g. Select all features within 300 metres of a road.

Specification
Technical description of the structure and schema associated with a specific dataset or product.

Spheroid
A surface generated by revolving an ellipse about one of its axes. Specifically used for a surface whose dimensions are chosen to approximate to the shape of the earth.

Spline
A term meaning a type of polyline created not by coordinate pairs but by anchors that influence the bearing of the line. A beizier curve and Bline are other examples.

Spot Height
A point on the earth's surface for which the height above a reference datum is known and which has been fixed by observation.

SQL
See Structured Query Language.

String
A set of items which can be arranged into a sequence according to a rule. See also Character String.

String
A sequence of coordinate pairs or triplets making up a line or link.

Structured Data
Data within which collections of features (of any type) form objects.

Structured Query Language
An international standard language for manipulating and interrogating relational databases. It is commonly used in querying spatial attributes in GIS. For example 'Select * from Map where value > 203'. It can also be extended to include spatial operations.

Supply Format
The file format in which the data is supplied to the customer. OS MasterMap data is only being supplied in GML.

Surveying
The determination of the absolute and relative positions of points, on or near the earth's surface , by means of measurement in the three elements of space; distance, direction and elevation, and hence their subsequent representation onto a plane surface, exhibiting them in their correct horizontal and vertical relationships.

Symbol
A graphic representation of a concept that has meaning in a specific context.

Symbol Feature
A feature represented by a graphical sign with a specific meaning e.g. triangulation pillar or bench mark.

Table
A representation of data in a database. It is organised into records (rows or tuples) and attributes (columns). The attributes for map data, such as area, number of residents for example will be stored in tables.

Tagged Image File Format
A popular image file format for storing scanned images. It is supported by the majority of image-editing programs running on a variety of computer platforms.

TCP-IP
See Transmission Control Protocol / Internet Protocol.

Terrier
See Land Terrier.

Text Attributes
A series of parameters defining the characteristics of the text displayed on a map. Text attributes include colour, font, size, location and angle.

Text String
The set of characters to be plotted as a text feature; it is indivisible in the data.

Textual Fidelity
The correctness of text within a geographic dataset.

Thematic
Depicting one or more specific topics or subjects e.g. Land use, rainfall, population density.

Thiessen Polygons
A method used to divide an area into polygons so that all locations closest to a particular sample point are enclosed within a single polygon. The boundary lines are defined at positions equidistant between two adjacent points. Also known as Dirichlet tesselations and Voronoi polygons.

TIFF
See Tagged Image File Format.

TIGER
See Topologically Integrated Geocoding and Referencing.

TOID
See Topographic Identifier.

Topographic Database
A database in which data relating to the physical features and boundaries on the earth's surface is held.

Topographic Identifier
A 16 digit number that uniquely identifies every feature. No intelligence (e.g. Its coordinate position) about the feature can be derived from either the allocated number or the process by which it is allocated. The TOID will remain with the feature throughout its life and will not be reassigned to a new feature when the existing feature is deleted.

Topographic Map
A map for the principle purpose of portraying and identifying the features of the earth.

Topography
The study of the physical features of the earth.

Topology
Properties of geometric forms that remain invariant when the forms are deformed or transformed by bending, stretching or shrinking. Among the topological properties of concern in GIS are connectivity, order and neighbourhood.

Transfer Format
The format used to transfer data consistently between computer systems. In general usage this can refer not only to the organisation of data, but also to the associated information, such as attribute codes which are required in orderto successfully complete the transfer.

Transfer Medium
The physical medium on which digital data is transferred from one computer system to another e.g. CD-ROM.

Triangulation Station
A permanently marked and fully documented control station whose position on the earth's surface has been established to a high accuracy both absolutely and in relative terms to other adjacent stations by means of angular or electronic distance measrement. Triangulation stations form the framework on which all survey and mapping techniques are based.

Tuple
A set of n coordinates representing a point in n-dimensional space, as defined by a spatial reference system. The British National Grid reference system is 2D only, so coordinate tuples consist of an easting and a northing coordinate.

UKSGB
See United Kingdom Standard Geographic Base.

UML
See Unified Modelling Language.

Unclipped (Data Supply)
All feature which lie wholly or partly within the query area are supplied and the full geometry of each of these features will be included in the supply. OS MasterMap data will only be supplied unclipped.

Unified Modelling Language
An OO notation for expressing anslysis and design. The notation is a collaboration between the athors of the three most populat OO methods and is becoming a de-facto standard among the OO development community. UML is an OMG standard.

Uniform Resource Locator
The way that the protocol, server, address and path are addressed to uniquely identify Internet resources.