 | Glossary for students M-Q |
Manhattan distance: The method used to calculate distance between cells in a raster data layer by counting the distance along the sides of the raster cells.
Manual digitizing: The process of digitizing maps and aerial photographs using a table digitizer.
Map algebra: A method of combining raster data layers. Mathematical operations are performed on individual cell values from two or more input raster data layers to produce an output value.
Map overlay: The process of combining the data from two or more maps to generate a new data set or a new map. This is a fundamental capability of GIS.
Map projection: A mathematical and/or geometric method used to transfer the spherical surface of the Earth onto a flat surface such as a map. Many different map projections exist, each with its own advantages and disadvantages.
Mapematics: See Map algebra''.
Mathematical model: A model that uses one or more of a range of techniques, including deterministic, stochastic and optimization methods.
METEOSAT: A geostationary weather satellite monitoring the whole of the western hemisphere.
Middleware: Technology that breaks down information into packets for exchange between servers and clients.
Modifiable areal unit problem (MAUP): A problem arising from the imposition of artificial units of spatial reporting on continuous geographic phenomena resulting in the generation of artificial spatial patterns.
Monte Carlo simulation: A statistical technique used to simulate the effects of random error in data analyses. Random noise'' is added to the input data and analyses run repeatedly to estimate the effects on the output data.
Multi-criteria evaluation (MCE): A method of combining several, possibly conflicting, criteria maps to derive suitability maps based on trade-off functions and user-specified criteria preference weights.
Multi-criteria modelling: See Multi-criteria evaluation (MCE)''.
Multimedia: Digital media presented in multiple forms, including text, pictures, sound and video
National Center for Geographic Information and Analysis (NCGIA): An organization set up with funding from the US National Science Foundation to lead US GIS research.
National transfer format (NTF): Standard data transfer format developed and used by the Ordnance Survey in the UK.
Natural analogue model: A model that uses actual events or real-world objects as a basis for model construction.
Natural language: Spoken or written language.
NAVSTAR: American GPS satellite constellation consisting of 24 satellites used for location fixing.
Network: (1) A special type of line entity used to represent interconnected lines that allow for the flow of objects (for example, traffic) or information (for example, telephone calls). (2) Two or more interconnected computers used to facilitate the transfer of information.
Neural networks: Classification systems that look for pattern and order in complex multivariate data sets. A key component of Artificial Intelligence (AI) techniques.
Node: Point entity representing the start or end point of a line or its intersection with another line.
Nuclear Industry Radioactive Waste Executive (NIREX): Organization set up to oversee the disposal of radioactive waste in the UK.
Object-oriented approach: Approach to organizing spatial data as discrete objects in a single map space.
Octree: Three-dimensional modification of the quadtree data structure.
Optical character recognition (OCR): Software used to recognize the shape of alphanumeric characters in a scanned image and convert these to ASCII text files.
Optimization model: A model that is constructed to maximize or minimize some aspect of its output.
Ordnance Survey: UK mapping agency.
PERT: Program evaluation and review technique. A project management tool.
Pilot project: An example software application that shows the potential of a larger application. This is often referred to as a demonstrator''. See also Prototyping''.
Pixel: A single cell in a raster data model. Short for picture element.
Planar co-ordinates: See Cartesian co-ordinates''.
Plotter: Output device used to draw maps and other diagrams from digital data.
Plug-ins: Software that works automatically when particular types of files are encountered by a web browser.
Point: A single ( x , y ) co-ordinate or pixel used to describe the location of an object too small to be represented as a polygon or area feature within the working scale of the GIS.
Point dictionary: Vector data structure in which all points are numbered sequentially and contain an explicit reference which records which co-ordinates are associated with which polygon.
Point-in-polygon overlay (PIP): The process of laying a point map over a polygon map to determine which points fall within which polygon.
Point mode digitizing: A method of manual digitizing whereby the operator decides where to record each co-ordinate.
Polygon: A multifaceted vector graphic figure used to represent an area and formed from a closed chain of points.
Polygon-on-polygon overlay: Process of overlaying two polygon maps to determine how the two sets of polygons overlap. There are three main types of polygon overlay: UNION, INTERSECT and IDENTITY.
Postal code: Non-geographic co-ordinate system consisting of alphanumeric codes used to increase the efficiency of mail sorting and delivery. Linked to geographic co-ordinates these can be a useful form of spatial reference.
Primary data: Data collected through firsthand observation. Field notes, survey recordings and GPS readings are examples of primary data.
Prototyping: An IT software development and project management methodology that uses prototype'' software applications to test ideas with potential users. See also Pilot project''.
Public land survey system (PLSS): Recursive division of land into quarter sections which can be used as a non-co-ordinate referencing system. Used in the western USA
Quadtree: A compact raster data structure in which geographical space is subdivided into variably sized homogeneous quarters.
Quaternary triangular mesh (QTM): A referencing system that tries to deal with irregularities on the Earth''s surface using a regular mesh of triangles. An alternative to the geographic (latitude and longitude) referencing system.
