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# Glossary of GIS Terminology Part 3

Isoline map - A map with the form of a surface shown by lines connecting points of equal value. A contour map is also an isoline map.

Isometric mapping - A function that preserves distances between certain points. Also called length-preserving mapping.

Isopleth map (Isoline map) - A map displaying the distribution of an attribute in terms of lines connecting points of equal value.

Jaggies - Jargon term for curved lines that have a stepped or saw-tooth appearance on a display device.

K-means - An iterative method of unsupervised classification (clustering). The n-dimensional raster space is divided into K clusters. The cluster means are used to determine cluster membership. After all cells are processed, new cluster means are determined and the process is repeated a predetermined number of times or until convergence is achieved.

Kilohertz or KHz - (CRT) A unit of frequency equal to one thousand cycles per second.

Kriging - Kriging is a method of interpolation named after a South African mining engineer named D. G. Krige who developed the technique in an attempt to more accurately predict ore reserves. Over the past several decades kriging has become a fundamental tool in the field of geostatistics. Kriging is based on the assumption that the parameter being interpolated can be treated as a regionalized variable. A regionalized variable is intermediate between a truly random variable and a completely deterministic variable in that it varies in a continuous manner from one location to the next and therefore points that are near each other have a certain degree of spatial correlation, but points that are widely separated are statistically independent (Davis, 1986). Kriging is a set of linear regression routines which minimize estimation variance from a predefined covariance model.

Label - A vector element that contains text used to identify a node, line, or polygon element.

Land cover - The materials that cover a study site, such as vegetation, bare soil, rock, sand, and water.

Land information system (LIS) - A geographic information system having, as its focus, data containing land records. Land records are broadly defined to include resource, land use, environmental impact, and fiscal data.

LANDSAT satellite - An American satellite series that collect multispectral images. At various times LANDSAT uses 1) a Return Beam Vidicon (RBV) device, 2) the Multispectral Scanning (MSS) device, and 3) the Thematic Mapping (TM) scanning device. LANDSAT also relays data from ground observation stations. LANDSAT was originally called the ERTS or Earth Resource Technology Satellite.

Large scale - A map scale that covers a relatively small area on the ground and has detailed labels. The term large refers to the fraction represented by the ratio of map distance to ground distance. For example, 1:500 (one map unit = 500 ground units.)

Latitude – It is a geographic coordinate that specifies the north-south position of a point on the Earth's surface. Latitude is an angle which ranges from 0° at the Equator to 90° (North or South) at the poles.

Layer - Refers to the various overlays of data, each of which normally deals with one thematic topic. These overlays are registered to each other by the common coordinate system of the database.

Least squares - A mathematical method for fitting a line or curve to a set of data points. Least squares minimizes the sum of the squares of the error term at each point.

Legend - The part of the drawn map explaining the meaning of the symbols used to code the depicted geographical elements.

Linear transform (map registration) - One kind of map registration sub object (Regist) that contains an object’s mathematical representation for its calibration solution (least squares) derived from a control point list.

Longitude – It is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Points with the same longitude lie in lines running from the North Pole to the South Pole. By convention, one of these, the Prime Meridian, which passes through the Royal Observatory, Greenwich, England, was intended to establish the position of zero degrees longitude. The longitude of other places was to be measured as the angle east or west from the Prime Meridian, ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. .

Map - (Cartography) A hand-drawn or printed document describing the spatial distribution of geographical features in terms of a recognizable and agreed symbolism. (Digital) The collection of digital information about a part of the Earth’s surface.

Map generalization - Process of reducing the detail of spatial features in a map layer. Often undertaken in conjunction with a reduction in map scale. This process is relatively easy for humans and relatively difficult for computers.

Map grid - A grid superimposed on a map to provide a coordinate system more convenient than that provided by the graticules.

Map projection - A device for representing all or part of a rounded surface on a flat sheet. Since this cannot be done without distortion, the cartographer must choose the map characteristic (area, shape, scale, direction) which is to be shown accurately at the expense of others. The map projection geometrically or mathematically generates the grid of lines of latitude and longitude. (See also Ellipsoid)

Map quadrangle or map quad - The geographic area covered by a map. One kind of map quadrangle is the 7.5’ x 7.5’ area that is covered by a standard USGS 7.5’ topographic map. Referring to a 7.5’ map quadrangle does not imply the presence of an actual paper map. The term may simply designate the area covered by electronically stored materials.

Map scale - The relationship that exists between a distance on a map and the corresponding distance on the Earth. It may be expressed as an equivalence, one inch equals 16 statute miles; as a fraction or ratio, 1:1,000,000; or as a bar graph subdivided to show the distance that each of its parts represents on the Earth.

MapGrafix - A computerized mapping system offering graphic and database management capabilities for digital mapping and GIS application. It operates on Apple Macintosh computers, developed by ComGrafix, Inc.

MapInfo - A desktop geographic information system (GIS) software product produced by Pitney Bowes Software (formerlyMapInfo Corporation) and used for mapping and location analytics. MapInfo allows users to visualise, analyse, edit, interpret, understand and output data to reveal relationships, patterns, and trends. MapInfo allows users to explore spatial data within a dataset, symbolize features, and create maps.

Mapping unit - A set of areas drawn on a map to represent a well-defined feature or set of features. Mapping units are described by the map legend.

Mercator projection - A map projection centered along the equator with evenly spaced meridians perpendicular to parallels spaced progressively farther apart poleward so that compass bearings are not distorted. A transverse mercator projection uses the same system of projection, but with the projection centered along a meridian to provide low distortion within a zone around the central meridian.

Merge - To combine items from two or more similarly ordered sets into one set that is arranged in the same order. In a GIS, to splice separate but adjacent mapped areas into a single data set.

Meridian - A great circle on the Earth’s surface that passes through the terrestrial poles.

Microstation GIS - A GIS marketed by Intergraph Corporation, which has the combination of the graphics capabilities of Microstation 32 with a user-selected relational database management system (Informix, Oracle, or Ingres). It has a core product, Microstation GIS Environment (MGE) which organizes and manages all information for the GIS operations.

Minicomputer - A medium sized general purposes single processor computer often used to control GIS.

Minute or ’ - The sixtieth part of a degree of angular measurement, often represented by the sign ’, as in 30’, read "30 minutes".USGS quadrangle maps are common in both 15 and 7.5 minute sizes. (See also Arcsecond)

MIPS - 1) Million Instructions per Second - A processor speed performance parameter. 2) Map and Image Processing System – A GIS marketed by MicroImages, Inc. It has both raster and vector data structure, and can be linked to a dBASE database.

Modeling - 1) Representation of the attributes of the Earth’s surface in a digital database. 2) The study of landscape processes using mathematical algorithms written in computer codes.

Modem - MOdulator-DEModulator. A translating device that links a terminal to a telecommunications network. An acoustic coupler is a modem that permits a terminal to communicate through the handset of a standard telephone instrument.

Module - A separate and distinct piece of hardware or software that can be connected with other modules to form a system.

Monochrome image - An image displayed in a single color or shades of a single color. Most monochrome computer displays use white, green, or amber, although any one color is possible.

Monument - Permanent physical structure marking the location of a survey point.

Mosaic - A large image assembled from raster object segments. Each segment may come from a different source and have a different cell size and angle of orientation. In automatic mosaicking, all the segments must be geometrically rectified and calibrated to a common coordinate framework. In manual mosaicking, the calibration framework can be established from control points in certain pieces, as long as the relative positions of the pieces that do not have control points can be inferred from pass points. (See also Tiling)

MOSS - Map Overlay and Statistical System. A pioneer vector-based geographic information system (GIS) developed and still widely used by groups in the USDI, especially the USF&WS and BLM. MOSS vector data files contain strings of coordinate pairs which describe closed polygonal areas, lines, and single point features. Common boundaries between adjacent polygons are duplicated in this data structure, once with each polygon.

MSS - Multi-Spectral Scanner. A sensing device on the LANDSAT satellite that collects simultaneous images over multiple ranges of the spectrum.

Multipurpose cadastre - The basic components of a multipurpose cadastre are a geodetic reference frame, a base layer that uses the geodetic reference frame for control, and a cadastral overlay that is controlled by references to both the geodetic reference frame and features on the base layer. Multipurpose cadastre systems also integrate a large number of other parcel records keyed to a unique parcel identifier. These ancillary records may include information used for legal reference (legal cadastre), data related to land valuation and taxation (fiscal cadastre), and information used for resource and facility management (resource cadastre).

Multisensor images – Co-registered images with the same cell size collected by different sensing devices. For example, a 10-meter SPOT panchromatic image can be co-registered with a resampled LANDSAT TM image so that their cells correctly match. This combination is called a multisensor image.

Multispectral images - Images optically acquired in more than one spectral or wavelength interval. Each individual image is usually of the same physical area and scale but of a different spectral band. The MSS and TM sensors aboard the LANDSAT satellite both collect simultaneous multispectral images. The TM sensor scans and stores seven individual images in spectral bands ranging from the blue wavelengths up to those in the thermal infrared.

Multitemporal images - Coregistered images collected at different times by the same device. For example, airvideo images collected one year apart, digitized, and warped to the same geometry are called multitemporal images and can be analyzed to map the changes between the dates.

Multivariable images - An image stored on more than one independent, coregistered raster. For example, a framegrabbed video image stored as independent red, green, and blue rasters is a multivariable image. So too, is any multitemporal, multispectral, or multisensor image.

NAPP aerial photographs - National Aerial Photography Program aerial photographs. USGS CIR high altitude aerial photographs. The NAPP series replaces the NHAP series. (See also NHAP)

NCGIA - National Center for Geographic Information and Analysis. A research center with sites at the University of California, Santa Barbara, University of Maine, and the State University of New York at Buffalo dedicated to research into GIS.

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.

Neighborhood analysis - In a GIS, a type of analytic process run on cell data in which a new value is assigned to each cell as a function of the values in surrounding cells.

NHAP aerial photographs - National High Altitude Program. NHAP is underwritten by the USGS and provides a publicly available collection of CIR aerial photographs 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.

Node - A point at which two or more lines meet; called an edge or vertex in graph theory.

Node element - A single point defined by a set of coordinates in space, and one of the types of elements in a vector object. Nodes may be lone points, or may occur as the terminal point at the end of (never in the middle of) one or more line elements.

Noise - Irregular variation, usually short range that cannot be easily explained or associated with major mapped features or processes.

Nominal image map - A preliminary map form that approximates an image map and that can usually be prepared using fully automated procedures. For example, image processing software can automatically extract a 7.5’ nominal image map from LANDSAT or SPOT satellite images in less than a minute using the positional and angular properties provided with the images. However, to convert it to an accurate image map, the user must introduce ground control points. A topographic map that has been scanned and assembled with a tiling process (but not yet calibrated) is another example of a nominal image map. (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.

Nonsolid color - A color produced by a pattern of differently colored dots that simulate the desired color. A solid color on one device (such as a 256-color monitor) may be nonsolid on another device. Also known as dithered color. (See Solid color)

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 thus usually cannot be normalized satisfactorily.

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 525-line 60-field 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.

Nugget variance - In a kriging procedure, the nugget variance is a spatially uncorrelated noise. It combines the residual variances of measurement errors together with spatial variations that occur over distances much shorter than the sample spacing, and that consequently cannot be resolved.

Objects - 1) A digital representation of all or part of an entity. 2) In object-oriented programming, an encapsulated module containing data and procedures.
Octree - A data structure designed to minimize storage for three-dimensional raster data.

Optimization - (In GIS display) The process by which a GIS chooses and assigns the best 256 display colors for the display of a three-raster RGB set in 8-bit contexts. With three 8-bit rasters (one with red spectral values, one with green, and one with blue), over 16 million colors are possible (far fewer typically occur). A GIS might then condense the set of actually occurring colors to a set of 4096, reserving 64 standard annotation colors, and then filling the remaining 192 positions in the color table with the most frequently occurring colors. The left-over colors from the 4096 might be assigned to their closest match in the color table. Optimization produces an excellent visual representation of most natural-color scenes.

Orthophotograph - An aerial photograph that has been scanned, rectified, and reconstructed so as to represent its features in a map projection or at least in a flat rectangular form without the usual distortions of geometry and perspective. Usually orthophotos are prepared from very high resolution stereo pairs.

Orthovideo - Airvideo images always include some geometric distortion from the camera, lens, movement, and perspective. Orthovideo images have been geometrically corrected with control points from a corresponding vector object. The control points are used to rubbersheet or warp the airvideo frame to yield a new raster with more map-like geometric properties.

Overlay - A transparent layer placed on an underlying layer or image. The overlay is where symbols, annotations, or image traces can be created or displayed without changing the underlying image.

Overlay analysis - The process of combining spatial information from two or more maps to derive a map consisting of new spatial boundaries.

Panchromatic image - An image collected in the broad visual wavelength range but rendered in graytone (black and white). The term has historically referred to a black and white photograph of a color scene. Since the SPOT satellite 10-meter images are collected over this broad visual spectral band and are usually rendered in black and white, these images are called panchromatic.
Parametric map - A map with certain criteria that, as a whole, describe a statistical population.

PC ARC/INFO - A vector-based Geographic Information System developed and marketed by ESRI, Inc.

PCIPS - A raster-based microcomputer image processing system. This is a menu-oriented entry-level system that runs on standard color display cards such as CGA and EGA.

Pel or picture element - The smallest graphic unit that can be displayed on the screen, usually a single-colored dot. Different display hardware allows for more or fewer pels on the screen, determining the display resolution that is possible. The more rows and columns of pels, the finer the image detail that can be resolved. (See also Pixel)

Photo interpretation - Analyzing, measuring, and categorizing chosen features from aerial photographs.

Photogrammetry - Photogrammetry is a measurement technology in which the three dimensional coordinates of points on an object is determined. This is achieved by stereoscopy, which is measurements made in two (or more) photographic images taken from different positions (different views).

Pit - A depression in the digital surface of a DEM, often caused by noise. The noise may result from short range variations on the digitized land surface (e.g., resulting from a cleared patch in a forest) or from the quantization of the original data.

Pixel depth or color depth - The number of data bits each pixel represents. In 8-bit contexts, the pixel depth is 8, and each display pixel can be one of 256 possible colors or shades of gray. With a 24-bit raster (or with three coregistered 8-bit rasters) the pixel depth is 24, and 16,777,216 colors are possible.

Pixel or picture element - The smallest element of an image that can be individually processed in a video display system. The text and images on a computer display are created by combinations of individual dots (pixels). Different display hardware allows for more or fewer pixels on the screen, determining the display resolution that is possible. The more rows and columns of pixels, the finer the image detail that can be resolved.

Plane coordinates - Coordinates specifying the locations of points in a plane. In cartography the plane usually is a projection of the Earth’s surface onto a flatten able cone or cylinder, and the x and y values scaled along the rectangular axes are called easting’s and northing’s, respectively.

Planimetric map - A map designed to portray the horizontal positions of features; vertical information is specifically ignored.

Plat map - A map representing property, subdivision, and political boundaries.

Plotter - A device for drawing maps and figures.

Point - A level of spatial measurement referring to an object that has no dimension. Examples include wells, weather stations and navigational lights.

Point data - In a vector structure, data consisting of single, distinct (x, y) coordinates. In a raster structure, point data is represented by single cells.

Polygon - A two-dimensional figure with three or more sides intersecting at a like number of points. In GIS systems, an area.

Polygon data - In a vector structure, data defined by an enclosing line or lines. In a raster structure, a group of contiguous cells containing identical values.

Polygon mapping - A cartographic display of regularly or irregularly shaped polygons and their attributes. Typically, this capability includes shading, symbology and numeric labeling, as well as a variety of other map cosmetic functions for generating alphanumeric labeling of polygons.

Polygonization - Process of connecting arcs or spaghetti to form polygons.

Pour point - (watershed analysis) The low point on the boundary ridge between two neighboring watersheds. It is the point through which water from one watershed would begin spilling over into its neighbor if it were completely filled.

Precision - Degree of detail in the reporting of a measurement. Generally refers to the number of significant digits of information.

Prime Meridian - The meridian on the Earth’s surface from which longitude is measured; generally the meridian of Greenwich, England.

Principal components analysis - A statistical technique for reducing an image’s dimensionality. Principal components chooses uncorrelated linear combinations of a set of rasters in such a way that each successively extracted linear combination, called a principal component, has a smaller variance. If the rasters have significant linear intercorrelations, the first few components will account for a large part of the total variance. (See Ordination)

Projection or map projection - A device for representing all or part of a rounded surface on a flat sheet. Since this cannot be done without distortion, the cartographer must choose the map characteristic (area, shape, scale, direction) which is to be shown accurately at the expense of others. (See also Ellipsoid)

Proximity analysis - A procedure that involves the creation of polygons or areas around randomly spaced point locations. It is carried out by dividing equally the distance between paired points, then generating perpendicular lines to these mid-way points which are then extended to intersect and form areas. This process is used for creating polygons, mapping, and analyzing qualitative data where a continuous coverage map is desired, but where contouring is not appropriate. It is possible to obtain pictorial displays of discontinuous data using this method.

Proximity map - A map that shows the distance from selected features by gradient shades of color.

Pseudo-color image - A color image that does not directly render the colors of the original image from individual red, green, and blue color values. A pseudo-color image could result from such processes as assigning colors to the gray levels in a grayscale image or assigning colors to a cluster map. (See also Composite color raster object)

Pseudo-random - (GPS) A signal with random-noise-like properties. It is a very complicated but repeated pattern of 1s and 0s.

Quad or quadrangle map - (Also Map quad and Map quadrangle). The geographic area covered by a map. One kind of map quadrangle is the 7.5’ x 7.5’ area that is covered by a standard USGS 7.5’ topographic map. Referring to a 7.5’ map quadrangle does not imply the presence of an actual paper map. The term may simply designate the area covered by electronically stored materials.

Quadrant - A quarter of a circle, 90 degrees.
UPDATED:  July 9, 2017