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The relationship of the position of a feature shown on a map to its true position.  Accuracy can be Absolute or Relative and defined mathematically.  For more detailed information refer to the Ordnance Survey website; h


Air Graphic (Air Ground) survey

A technique of using enlarged vertical aerial photographs to assist the updating of maps by graphic survey methods.



The science and art of map making.


Chief Surveyor

A middle management post within Ordnance Survey responsible for a number of headquarters based staff with a specific production role in the maintenance of the national mapping archive.  Up to 31 March 1999 the title also applied to field based middle managers, thereafter known as Production Group Managers, and from 2003 onwards as Region Managers and Assistant Region Managers.


Control point

A physically monumented point for which coordinates of a known quality have been defined (for example, triangulation station).


Definitive Map


A map that is a legal record of a public’s rights to walk, ride or drive on public rights of way.
NOTE: The duty of the responsible surveying authority is to show on the Definitive Map all footpaths, bridleways, restricted byways, BOATs* and RUPPs** in its area, whether urban or rural. Definitive Maps are prepared everywhere in England and Wales except in the area of the former London County Council (LCC) where their preparation is optional.
BS7666, part 4, 1996.
* BOAT = “Byway Open to All Traffic”
** RUPP = “Road Used as Public Path”, now superseded by “Restricted Byway”


Definitive Statement

The Definitive Statement is a legal textual record which accompanies the Definitive Map.
NOTE: The Definitive Map and Statement provide conclusive evidence (that is, evidence that can be used in court) of the existence of public rights of way and their extent, legal conditions and limitations.
BS7666, part 4, 1996.


Digital Field Update

A system of updating Digital maps in the surveyor’s field office.


Digital Map

A map in a form suitable for storage, transmission and manipulation by computers.


Electronic Distance Measurement (EDM)


Distance measurement instruments that transmit narrow beams of light that are reflected back to the receiver.  A microprocessor then converts the phase differences of the transmitted and received light waves into a distance measurement.  These instruments can measure long distances to within a few millimetres at the press of a button.


Geometric Fidelity


The principle of Geometric Fidelity is that any real-world alignment or shape must be accurately reflected in the data to the required specification.  Detail that is square on the ground must be represented as square in the data; shapes must be accurate; alignments that are straight in real life must be represented as straight lines within the data; lines of sight that pass through points on the ground should pass through the map positions of the corresponding points; adjacent features should be in sympathy with each other as regards alignment, distance apart and orientation.


Geospatial Content Improvement Programme (GCIP)


Minor changes in urban areas have not been systematically picked up by Ordnance Survey over the last 30 to 40 years due to the priority it has  given to recording significant topographic changes throughout Great Britain.  Ordnance Survey is now embarking on a Geospatial Content Improvement  Programme to improve the representation and scope of the data shown on the MasterMap Topography Layer in urban areas, mainly affecting 1:1250 mapping.  OS aims to capture around 14,000 km2 of urban geography over an estimated three years, using high-resolution imagery from aerial photography.  The existing map detail will be compared side by side with the aerial imagery, plotting any new features and moving those existing features which fail the set quality standards. This will be supplemented by the work of surveyors in the field where detail is obscured or unclear.  GCIP follows the Positional Accuracy Improvement (PAI) programme which principally affected 1:2500 mapping.


Global Positioning System (GPS)


A radio navigation system that allows land, sea, and airborne users to determine their exact location in all weather conditions, anywhere in the world.  GPS is used to support a broad range of military, commercial, and consumer applications.  24 GPS satellites are in orbit.  Each satellite contains a computer, an atomic clock, and a radio. With an understanding of its own orbit and the clock, the satellite continually broadcasts its changing position and time.  On the ground a GPS receiver contains a computer that fixes its own position by calculating the distance to three or more satellites.  Survey quality GPS receivers can fix positions to within a few centimetres.


Graphic survey

A method of survey based upon reproducing the relationship between lines of sight, short measurements and the construction of right angles.


Instrumental survey

Any form of survey using high precision optical or electronic instruments.


Land survey

The science and mathematics of measuring the Earth and features on it, and recording the data in a methodical way.


Large scale survey (map)

A survey (map) at one of the basic scales of 1:1250, 1:2500 or 1:10 000.


National Grid


A rectangular grid used on most modern Ordnance Survey maps to enable each object on the map to be uniquely referenced in terms of distance east and distance north of a defined origin (see Ordnance Survey Maps - a descriptive manual by J. B. Harley, Ordnance Survey, Southampton 1975).



National Interest Mapping Services Agreement; NIMSA was an agreement between government and Ordnance Survey for supply of survey and mapping services needed in the national interest.  Under this agreement Ordnance Survey was charged by Government with maintaining the definitive, consistent record of the natural, man-made and cultural landscape of Britain up to date, and with disseminating this information to customers in government and elsewhere. This involved carrying out some activities that were not commercially viable.  NIMSA was terminated in December 2006 since when Ordnance Survey has been required to be self financing.


Optical tacheometry

A method of measuring distances by use of a theodolite or level.
Ordnance Survey

The National Mapping Agency of Great Britain.


Ordnance Survey Location Map

An updated name for OS Sitemap® (see below)


OS MasterMap®

OS MasterMap® was designed by Ordnance Survey as an intelligent digital map and digital representation of the real world, to be used with geographical information systems (GIS) and database systems. It is a business tool to manage information, aid analysis and speed the decision making process. It provides intelligent data with real-world objects represented as explicit features, each identified by a unique number.


OS Sitemap®

An Ordnance Survey product which is a printout from the Ordnance Survey digital mapping database of the latest available large scale survey.

Pan-Government Agreement 

The Pan-Government Agreement (PGA) was managed on behalf of central government by the Intra-Governmental Group on Geographical Information (IGGI).  In general terms, membership of the agreement was open to organisations that employ civil servants.  The range of potentially eligible organisations was broad and included crown and non-crown bodies, government departments, executive agencies and sponsored bodies.  This agreement was replaced by the Public Sector Mapping Agreement (PSMA) on 1st April 2011.


A high precision technique, used world-wide, for survey applications using photography, (usually vertical, aerial photographs).


Positional Accuracy Improvement (PAI)

The Positional Accuracy Improvement programme dealt with improving the Absolute Accuracy of 1:2500 scale mapping from 1:2500 scale Overhaul accuracies to either 1:1250 scale Resurvey standards (for the built-up areas of defined rural towns) or 1:2500 scale Resurvey standards (the remaining rural areas).  However, any surveyed changes also conformed to the Geometric Fidelity and Relative Accuracy of those standards of survey.  For more detailed information refer to the Ordnance Survey website;



The ability of an instrument or process to repeat measurements to a stated tolerance.




The Portable Revision and Integrated Survey Module (PRISM) is an improved version of the Portable Interactive Editing System (PIES); a portable Pen Computer which enables Ordnance Survey surveyors to update and edit Digital Maps at the time of survey.


Production Group Manager


From 1999 up to 2003 a middle management post within Ordnance Survey responsible for a number of field based staff with a specific production role in the maintenance of the national mapping archive.  Up to 31 March 1999 these managers were known as Chief Surveyors, and after 1st April 2003 as Region Managers and Assistant Region Managers.


Public Sector Mapping Agreement (PSMA)

From 1st April 2011 the Public Sector Mapping Agreement (PSMA) replaced the Pan Government Agreement. Under PSMA public sector organisations in England and Wales have access to most of Ordnance Survey’s mapping data under a single agreement for the first time.



A new survey, not based upon earlier surveys.



The updating of an earlier survey.




The relationship between a distance measured on the map and the equivalent distance measured on the ground, for example, a scale of 1:10 000 means that a measurement of one unit on the map represents a measurement on the ground of 10 000 units.



Survey Information on Microfilm.  A copy of updated Ordnance Survey large scale mapping taken from a microfilm copy of the surveyor’s working document for security and archive purposes.



Superplan Instant Printout. A copy of updated Ordnance Survey large scale mapping taken from the digital archive for security and archive purposes.



A copy of a large scale Ordnance Survey map printed on demand from the latest Ordnance Survey Landline data.



Supply of Unpublished Survey Information.  A copy of the Ordnance Survey surveyor’s Master Survey Document produced on demand for a customer.



An instrument used for measuring angles in the horizontal and vertical planes.



The maximum acceptable difference between measurements on a map and the equivalent true measurements on the ground.


Topographic map

A map which depicts physical features on the ground at the time of survey, within the limitations imposed by the particular scale and specification of the map. A topographic map does not show property boundaries.



The process of quantifying the accuracy and precision of a survey.