GIS Glossary/N

GIS Glossary

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NAD 1927
Acronym for North American Datum of 1927. The primary local horizontal geodetic datum and geographic coordinate system used to map the United States during the middle part of the twentieth century. NAD 1927 is referenced to the Clarke spheroid of 1866 and an origin point at Meades Ranch, Kansas. Features on USGS topographic maps, including the corners of 7.5-minute quadrangle maps, are referenced to NAD27. It is gradually being replaced by the North American Datum of 1983.

NAD 1983
Acronym for North American Datum of 1983. A geocentric datum and graphic coordinate system based on the Geodetic Reference System 1980 ellipsoid (GRS80). Mainly used in North America, its measurements are obtained from both terrestrial and satellite data.

nadir
In aerial photography, the point on the ground vertically beneath the perspective center of the camera lens.

NAICS
Acronym for North American Industry Classification System. A system for classifying individual business locations by their types of economic activity. The statistics agencies of Canada, Mexico, and the United States collaborated on NAICS to standardize the industry statistics produced by the three countries. NAICS is used as an identification system by all federal statistical agencies, as well as many state and local agencies, trade associations, private businesses, and other organizations. NAICS replaced Standard Industrial Classification (SIC) codes in 1997.

NaN
Acronym for not a number.

N-ary association
A UML term that describes how two classes have a relationship with one or more other classes. In an N-ary association, instances of the classes in question usually exist together, but can exist on their own. For example, a three-way valve usually has one size of pipe coming in and two other sized pipes going out. Before the pipes and valve are connected into the water system they are separate parts; therefore, they have an N-ary association.

National Geodetic Vertical Datum of 1929
The datum established in 1929 by the U.S. Coast and Geodetic Survey as the surface against which elevation data in the United States is referenced.

National Spatial Data Infrastructure
A federally mandated framework of spatial data that refers to U.S. locations, as well as the means of distributing and using that data effectively. Developed and coordinated by the FGDC, the NSDI encompasses policies, standards, procedures, technology, and human resources for organizations to cooperatively produce and share geographic data. The NSDI is developed by the federal governments; state, local, and tribal governments; the academic community; and the private sector.

natural breaks classification
A method of manual data classification that seeks to partition data into classes based on natural groups in the data distribution. Natural breaks occur in the histogram at the low points of valleys. Breaks are assigned in the order of the size of the valleys, with the largest valley being assigned the first natural break.

natural neighbors
An interpolation method for multivariate data in a Delaunay triangulation. The value for an interpolation point is estimated using weighted values of the closest surrounding points in the triangulation. These points, the natural neighbors, are the ones the interpolation point would connect to if inserted into the triangulation.

navigate
To interactively change the observer's or target's position using a tool designed for this purpose, such as the navigate or fly tool. There are three contexts in which a user can navigate: in a scene of ArcScene, in a preview of ArcCatalog, and in a globe of ArcGlobe.

navigation
The combined mental and physical activities involved in traveling to a destination, often a distant or unfamiliar one. Navigation comprises wayfinding and locomotion.

Navstar
The name of the U.S. Department of Defense's Global Positioning System (GPS).

nearest neighbor resampling
A technique for resampling raster data in which the value of each cell in an output raster is calculated using the value of the nearest cell in an input raster. Nearest neighbor assignment does not change any of the values of cells from the input layer; for this reason it is often used to resample categorical or integer data (for example, land use, soil, or forest type), or radiometric values, such as those from remotely sensed images.

neatline
The border delineating and defining the extent of geographic data on a map. It demarcates map units so that, depending on the map projection, the neatline does not always have 90-degree corners. In a properly made map, it is the most accurate element of the data; other map features may be moved slightly or exaggerated for generalization or readability, but the neatline is never adjusted.

neighborhood
On a raster, an analysis boundary or processing window within which cell values affect calculations and outside which they do not. Filters are used mainly in cell-based analysis where the value of a center cell is changed to the mean, the sum, or some other function of all cell values inside the filter. A filter moves systematically across a raster until each cell has been processed. Filters can be of various shapes and sizes, but are most commonly three-cell by three-cell squares.

neighborhood functions
Methods of defining new values for locations using the values of other locations within a given distance or direction.

neighborhood statistics
The computation of an output raster where the output value at each cell location is a function of the value at that cell location and the values of the cells within a specified neighborhood around the cell.

NetBeans IDE
An open-source development environment that supports all Java application types.

network
An interconnected set of points and lines that represent possible routes from one location to another. For geometric networks, this consists of edge features, junction features, and the connectivity between them. For network datasets, this consists of edge, junction, and turn elements and the connectivity between them. For example, an interconnected set of lines representing a city streets layer is a network.

network analysis
Any method of solving network problems such as traversability, rate of flow, or capacity, using network connectivity.

network analysis class
In ArcGIS Network Analyst, a feature class or table containing network analysis objects that is stored within a network analysis layer. Network Analyst solvers read input from, and write output to, network analysis classes.

network analysis layer
A composite layer that contains the properties and network analysis classes used in the analysis of a network problem, and the results of the analysis.

network analysis object
In ArcGIS Network Analyst, a feature or row in a network analysis class. Network analysis objects are used as input and written as output during network analysis. A network location is a specific type of network analysis object that has a defined position on a network dataset.

network ancillary role
An auxiliary or additional function performed by a junction feature within a geometric network. Junction features can act as sources or sinks for calculating flow direction. If a junction is a source or a sink, it is said to have an ancillary role in the network.

network attribute
A type of attribute associated with a network element in a network dataset. Network attributes are used to help control flow through a network (similar to a weight in a geometric network). All network elements in a network dataset have the same set of attributes. There are four types of network attributes: cost, descriptor, hierarchy, and restriction.

network dataset
A collection of topologically connected network elements (edges, junctions, and turns) that are derived from network sources, typically used to represent a linear network, such as a road or subway system. Each network element is associated with a collection of network attributes. Network datasets are typically used to model undirected flow systems.

network element
A component in a network dataset: an edge, junction, or turn. All elements in a network dataset share the same set of network attributes. Network elements are used to model topological relationships in undirected flow networks such as traffic flow systems. Network elements are generated from point, line, and turn features. When the network dataset is built, point features become junctions, line features become edges, and turn features become turn elements.

network feature
A component in a geometric network: an edge or a junction. Features in a geometric network are used to model topological relationships, typically in directed flow networks such as hydrologic or utility systems. Network features are generated from points and lines when the geometric network is built: point features become junctions, and line features become edges.

network layer
A layer that references a network dataset. In a geodatabase, a network dataset is a collection of network elements (edges, junctions and turns) that are derived from network sources.

network location
A geographic position in a network system.

node
A connecting point in a geometric network, such as an intersection or interchange of a road network, confluence of streams in a hydrologic network, or switch in a power grid.

network port
A number that is used to specify direct communication over a network to an Internet application.

network solver
A function that performs network analysis based on a set of network data.

network source
Feature classes in a geodatabase that are used to generate and define a network dataset.

network trace
A function that performs network analysis on a geometric network. Specific kinds of network tracing include finding features that are connected, finding common ancestors, finding loops, tracing upstream, and tracing downstream.

neural network
A computer architecture modeled after the human brain and designed to solve problems that human brains solve well, such as recognizing patterns and making predictions from past performance. Neural networks are composed of interconnected computer processors that calculate a number of weighted inputs to generate an output. For example, an output might be the approval or rejection of a credit application. This output would be based on several inputs, including the applicant's income, current debt, and credit history. Some of these inputs would count more than others; cumulatively, they would be compared to a threshold value that separates approvals from rejections. Neural networks "learn" to generate better outputs by adjusting the weights and thresholds applied to their inputs.

new store analysis
A process that finds a potential location for a new store by calculating the centroid of a group of customers.

NGVD 1929
The datum established in 1929 by the U.S. Coast and Geodetic Survey as the surface against which elevation data in the United States is referenced.

NGVD29
The datum established in 1929 by the U.S. Coast and Geodetic Survey as the surface against which elevation data in the United States is referenced.

NMEA
Acronym for National Marine and Electronics Association. A nonprofit association composed of manufacturers, distributors, dealers, educational institutions, and others interested in peripheral marine electronics occupations. The NMEA has created a standard that defines an electrical interface and data protocol for communications between marine instrumentation that has been adopted as an industry standard by the GPS industry.

NoData
In raster data, the absence of a recorded value. NoData does not equate to a zero value. While the measure of a particular attribute in a cell may be zero, a NoData value indicates that no measurements have been taken for that cell at all.

node
In a geodatabase, the point representing the beginning or ending point of an edge, topologically linked to all the edges that meet there.

noise
In remote sensing, any disturbance in a frequency band.

nominal data
Data divided into classes within which all elements are assumed to be equal to each other, and in which no class comes before another in sequence or importance; for example, a group of polygons colored to represent different soil types.

nonsimple polygon
A polygon that violates topological integrity by crossing its own boundary (usually by making a small loop).

nonspatial data
Data without inherently spatial qualities, such as attributes.

normal distribution
A theoretical frequency distribution of a dataset in which the distribution of values can be graphically represented as a symmetrical bell curve. Normal distributions are typically characterized by a clustering of values near the mean, with few values departing radically from the mean. There are as many values on the left side of the curve as on the right, so the mean and median values for the distribution are the same. Sixty-eight percent of the values are plus or minus one standard deviation from the mean; 95 percent of the values are plus or minus two standard deviations; and 99 percent of the values are plus or minus three standard deviations.

normal form
A set of guidelines for designing table and data structures in a relational database. When followed, normal form guidelines prevent data redundancy, increase database efficiency, and reduce consistency errors. A database is said to be in first normal form (1NF), second normal form (2NF), third normal form (3NF), and so on, depending on the level of normal form guidelines followed in its design. In practice, 3NF is commonly used, but higher levels are rarely used.

normal probability distribution
A theoretical frequency distribution of a dataset in which the distribution of values can be graphically represented as a symmetrical bell curve. Normal distributions are typically characterized by a clustering of values near the mean, with few values departing radically from the mean. There are as many values on the left side of the curve as on the right, so the mean and median values for the distribution are the same. Sixty-eight percent of the values are plus or minus one standard deviation from the mean; 95 percent of the values are plus or minus two standard deviations; and 99 percent of the values are plus or minus three standard deviations.

Normal template
The template that is automatically loaded in ArcMap and contains all the standard toolbar and command default settings. User interface customization that is saved in the Normal template is loaded each time ArcMap is launched.

normalization
The process of organizing, analyzing, and cleaning data to increase efficiency for data use and sharing. Normalization usually includes data structuring and refinement, redundancy and error elimination, and standardization.

North American Datum of 1927
The primary local horizontal geodetic datum and geographic coordinate system used to map the United States during the middle part of the twentieth century. NAD 1927 is referenced to the Clarke spheroid of 1866 and an origin point at Meades Ranch, Kansas. Features on USGS topographic maps, including the corners of 7.5-minute quadrangle maps, are referenced to NAD27. It is gradually being replaced by the North American Datum of 1983.

North American Datum of 1983
A geocentric datum and graphic coordinate system based on the Geodetic Reference System 1980 ellipsoid (GRS80). Mainly used in North America, its measurements are obtained from both terrestrial and satellite data.

North American Industry Classification System
A system for classifying individual business locations by their types of economic activity. The statistics agencies of Canada, Mexico, and the United States collaborated on NAICS to standardize the industry statistics produced by the three countries. NAICS is used as an identification system by all federal statistical agencies, as well as many state and local agencies, trade associations, private businesses, and other organizations. NAICS replaced Standard Industrial Classification (SIC) codes in 1997.

north arrow
A map symbol that shows the direction of north on the map, thereby showing how the map is oriented.

northing
The distance north of the origin that a point in a Cartesian coordinate system lies, measured in that system's units.

NOTAM
Acronym for Notice to Airmen. An advisory bulletin containing information about the National Airspace System, typically time-sensitive information between publishing cycles, or corrections to published documents and charts.

notice to airmen
An advisory bulletin containing information about the National Airspace System, typically time-sensitive information between publishing cycles, or corrections to published documents and charts.

notice to mariners
A periodical update to existing nautical charts, issued by maritime authorities.

NSDI
Acronym for National Spatial Data Infrastructure. A federally mandated framework of spatial data that refers to U.S. locations, as well as the means of distributing and using that data effectively. Developed and coordinated by the FGDC, the NSDI encompasses policies, standards, procedures, technology, and human resources for organizations to cooperatively produce and share geographic data. The NSDI is developed by the federal governments; state, local, and tribal governments; the academic community; and the private sector.

NSDI Clearinghouse Network
A community of digital spatial data providers that maintain NSDI Clearinghouse Nodes as part of the U.S. National Spatial Data Infrastructure.

NSDI Clearinghouse Node
An Internet server that hosts a collection of metadata and data maintained and stored on a computer server by a data provider. An NSDI Clearinghouse Node provides information about geographic data within the data provider's areas of responsibility. Nodes must host FGDC-compliant metadata and data and use a common access protocol.

NTM
Acronym for Notice to Mariners</I>. A periodical update to existing nautical charts, issued by maritime authorities.

nugget
A parameter of a covariance or semivariogram model that represents independent error, measurement error, or microscale variation at spatial scales that are too fine to detect. The nugget effect is seen as a discontinuity at the origin of either the covariance or semivariogram model.

null constraint
A DBMS-defined restriction specifying that a column cannot contain a null value.

null hypothesis
A statement that essentially outlines an expected outcome when there is no pattern, no relationship, and/or no systematic cause or process at work; any observed differences are the result of random chance alone. The null hypothesis for a spatial pattern is typically that the features are randomly distributed across the study area. Significance tests help determine whether the null hypothesis should be accepted or rejected.

null value
The absence of a recorded value for a field. A null value differs from a value of zero in that zero may represent the measure of an attribute, while a null value indicates that no measurement has been taken.