N
NAPP airphotos
National Aerial Photography Program airphotos. USGS CIR high altitude airphotos. The NAPP series replaces the NHAP series. (See also: NHAP airphotos)
NASA
National Aeronautics and Space Administration.
NAT
Node Attribute Table. A table containing attributes for node coverage features. For each node, the NAT contains a reference to one of the arc it connects to, an internal node sequence number and node feature identifier.
navigation
Moving a selection highlight or location cursor with a mouse or keyboard through the levels of a menu and window system.
ND, ND6 and ND7
Normalized Difference. Vegetation index computations developed for use with Landsat MSS. These vegetation indices are now commonly used with any image that has the required spectral bands. The bands required are approximately equivalent to the red and the photo-infrared spectral bands measured by color-infrared film. The ND6 index used MSS band 6, and ND7 uses band 7. Since these two Landsat MSS infrared bands are so highly correlated, similar results are possible using either of the computations or with any images that have an equivalent photo-infrared spectral band. Good color-infrared image sources for processing into an ND or green biomass raster include Landsat MSS and TM, SPOT CIR, 35mm CIR film, 9" CIR film, and CIR video.
nearest neighbor sampling/interpolation
Resampling a source raster to yield a new raster with a different cell size, raster orientation, and/or internal geometry by computing the distance between the center of each cell in the output raster and the 4 nearest cells in the input raster. The data value for the closest input cell is assigned without alteration to be the data value of the output cell. Therefore, the input value of one input cell may be assigned to more than one output cell. It also means that some input cells may not be transferred at all to the output raster. These undersampling and oversampling situations occur when the cell sizes of the input and output raster are different.
For example, a resampled output raster which is coparallel to the input raster but which has cells half as big, will repeat the input values in a 2 x 2 cell pattern. However, since nearest neighbor resampling does not mathematically compute the new cell's value, it is the only suitable choice for rasters that are not mathematically continuous such as land cover maps. With such maps, mathematical resampling (like bilinear, or cubic convolution) is totally incorrect since mean values cannot be computed.
Network
1. An inter connected set of arcs representing possible paths for the movement of resources from one location to another.
2. A coverage representing linear features containing arcs or a route system. Also known as network coverage.
3. When referring to computer hardware systems, a local area network (LAN) or a wide area network.
NETWORK
The ARC/INFO software product that performs address matching/geocoding, allocation, renting and pathfinding across linear networks.
NHAP airphotos
National High Altitude Program. NHAP is underwritten by the USGS and provides a publicly available collection of CIR airphotos covering the United States in print or transparency format.
nibble
A data element made up of 4 bits and having 16 possible values. Nibbles are stored two to a byte.
NOAA
National Oceanographic and Atmospheric Administration.
Node
1. The beginning and ending location of an arc. A node is topologically linked to all arcs that meet at the node.
2. In Graph theory, the location at which three or more lines connect.
3. The three cornered point of each triangle in a tin. Every sample points input to a tin becomes a node in the triangulation. A triangle node is topologically linked to all triangles that meet at the node.
node element
A vector element required for topology that has no attributes except position; nodes occur at the ends of all lines and at all line intersections.
nominal image map
A preliminary map form that approximates an image map and that can usually be prepared using fully automated procedures. (See also: image map.)
non-interlaced video
Video signal formats used in some new display boards and monitors. A non-interlaced video display board refreshes the whole display every 1/60 of a second. It does not intersplice fields but paints each successive line from top to bottom of the screen. Since the line refresh is twice as fast as standard video technology, the picture and lines do not noticeably decay between frames. Non-interlaced video is not standard, so if non-interlaced technology is chosen, extra care must be taken to match the monitor and the display board.
normalized contrast
See - contrast.
Normalized Difference
See - ND
normalized histogram
A histogram whose distribution has been adjusted so as to have as close to a normalized (bell-shaped) distribution as possible. The data value that occurs most frequently will be near the center of the histogram. Multimodal histograms are those which have two or more significant peaks in their distribution and cannot usually be satisfactorily normalized.
northing
A rectangular (x,y) coordinate measurement of distance north from an east-west reference line, usually the equator or other parallel used as the axis of origin for a map zone or projection. False northing is an adjustment constant added to coordinate values to eliminate negative numbers.
NTSC video
National Television Standards Committee video. The standard format used by all American home video equipment (like VCR recorders and television sets). All the necessary color information is encoded in a single interlaced signal which is often called composite color video.
NWI
National Wetlands Inventory conducted by the USF&WS.