Geographic Information Systems: A Glossary Charles R. Blinn, Lloyd P. Queen and Les W. Maki

Copyright ©  2009  Regents of the University of Minnesota. All rights reserved.

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• hard copy. An analog image of a map or diagram (e.g., a paper map produced by a printer or plotter) generated from a digital data set.
• hierarchical database. A method of structuring data or other information so that the units of data storage are connected by a hierarchically defined pathway.
• horizontal control. A network of stations of known geographic or grid positions referenced to a common horizontal datum, which controls the horizontal positions of mapped features with respect to parallels and meridians or northing and easting grid lines shown on the map.
• image processing. Computerized routines for information extraction (e.g., pattern recognition, classification) from remotely sensed images to obtain categories of information about specific features.
• import. Process of bringing data or software from one system into another.
• infrastructure. Human-made systems that provide any or all of the normal public services to an urban area (e.g., water supply, sewage, utilities, traffic control).
• ink jet plotter. A plotter that creates images by projecting a jet of ink onto the paper.
• input. (1) Data that have been entered into a computer system. (2) To enter data into a computer.
• interpolation. The process of estimating the value of an unsampled data point for a given x,y,z location based on the values of surrounding sampled data points.

• intersection. The coexistence of points at a specific geographic location; the set of all objects common to two or more intersecting sets.
• intervisibility functions. Planning tool used for siting features in a landscape through application of digital elevation data. It shows what can be "seen" from specified target locations. It can map the area visible from a scenic lookout or the area that can be detected by a radar antenna. It can show how a road or cleared land can be effectively hidden from view. Sometimes referred to as viewshed modeling or viewshed mapping.
• island. A polygon lying completely within another and not sharing a common boundary (e.g., an island in a lake).
• isoline map. See isopleth map.
• isopleth map. A map displaying the distribution of an attribute in terms of lines connecting points of equal value (e.g., a contour map).

• item. A single attribute descriptor or characteristic of a feature (e.g., an address for a house in an attribute table that contains information about houses in a community). Commonly displayed as a column in an attribute table. Contrast with record.
• kriging. An interpolation technique for obtaining statistically unbiased estimates of surface elevations from a set of control points. Pronounced creeging.
• label. A unique name or other nominal code assigned to identify the geographic representation of a map feature. It is distinguished from attribute data by serving as the unique identifier for geographic features (e.g., label: Jones Lake; attributes: area, depth, water quality).
• labeling. The process of assigning unique labels to polygons.
• land information system (LIS). A special type of GIS that manages and analyzes data related to land ownership (e.g., tax parcels, urban infrastructure, property assessment). A GIS used for municipal or county level applications is typically structured as an LIS. Data stored in an LIS are commonly recorded very accurately on a large-scale map (e.g., at scales of 1:1,000 to 1:10,000).
• land record. A document stored in a public file that contains the definitive statement of some characteristic of a piece of land that is a matter of public interest.
• LANDSAT. The generic name for a series of natural resource scanning satellites launched by the United States beginning in 1972.
• large scale. A map scale that covers a relatively small area on the ground and has a high level of detail. A small area of the earth's surface on one page is a large-scale map (i.e., a 1:500 map where 1 map unit equals 500 ground units is large scale compared with a 1:1,000,000 map). Contrast with small scale.
• latitude. A system of referencing relative north-south locations on the earth's surface. It is measured in degrees, minutes, and seconds north or south of the equator to the poles.
• layer. A logical separation of mapped information representing a theme (e.g., roads, soils, vegetative cover). Layers are registered to each other by control points and the common coordinate system of the database.
• line. A set of ordered coordinates that represent the shape of a linear geographic feature. It has a length and direction but no area. Examples include streams, roads, and telecommunication lines.
• lineage. Information about the source of data, its origin, accuracy, and scale that is normally kept in the data dictionary.
• longitude. A system of referencing relative east-west locations on the earth's surface. It is measured in degrees, minutes, and seconds east or west of the "Prime Meridian" which runs through Greenwich, England.
• macro. A set of instructions written in a high-level programming language that manipulate the commands in a GIS to perform specific predefined tasks or processes. Macros typically provide enhanced user access both to limited portions of an extensive GIS database as well as to certain GIS analysis tools or procedures. Sometimes called "shells."

The map of Minnesota is at a relatively larger scale than the map of the U.S.A. (See definition below.)

• map. A two-dimensional abstract graphic representation of the earth's surface that displays spatial relationships among features, generalizes their appearance to simplify them for the purpose of communication, and applies symbols to aid in interpretation.

• map algebra. Process of adding, subtracting, multiplying, and dividing maps by applying mathematical operations to map themes. Map algebra utilities allow the user to specify mathematical relationships between map layers. For example, a new map can be generated by determining the difference in elevation between a topographic map and the corresponding map of the water table.
• map analysis. See spatial analysis.
• map extent. The rectangular limits (xmin, ymin, xmax, ymax) that include all the features displayed on a graphics display terminal or on a plotted map.
• map generalization. The process of reducing detail on a map.
• map projection. See projection.
• map theme. See theme.
• merge. To take two or more maps or data sets and combine them together into a single, coherent map or database without redundant information.
• metadata. See data dictionary.
• model. A set of rules and procedures that represent a view of reality for conducting spatial analysis to generate a result.
• monument. A ground surveyed point of known x,y,z coordinates that is assumed to be correct for general mapping purposes.
• mosaic. Process of assembling GIS database files for adjacent areas into a single file.
• NAD 27. Datum used as the base level for topographic information, as established by the North American Datum, 1927.
• NAD 83. Datum used as the base level for topographic information, as established by the North American Datum, 1983.
• National Center for Geographic Information and Analysis (NCGIA). A center funded by the National Science Foundation that is jointly headquartered at the University of California, Santa Barbara, the University of Maine, Orono, and the State University of New York at Buffalo. The Center encourages the development of quality GIS education programs in universities in the United States and worldwide. It developed a core curriculum; a set of teaching materials for a three-course sequence in GIS. It also sponsors workshops, seminars, and meetings and produces technical publications related to GIS.
• neatline. A border line commonly drawn around the extent of a plotted map.
• needs analysis . See user requirements analysis.
• neighborhood analysis. Analytical technique to determine whether a set of areas (polygons) are situated next to each other and to examine their interrelationships.
• network analysis. Technique used to conduct analyses on a set of points (nodes) and lines that are connected to each other.
• node. A point at which two or more arcs or lines meet. Also the distinct point in a feature where lines begin and end. They are required in vector GIS to define topology.
• northing. See easting.
• object. A single, identifiable unit or entity. An object can comprise other, smaller objects.
• object oriented. The intrinsic representation and storage of real world entities in a GIS database rather than the use of cells, points, lines, or polygons to store the object.
• orthophotograph. An aerial photograph that has the distortion due to tilt, curvature, and ground relief corrected.
• orthophoto quad. A photomap made from an assembly of orthophotographs.
• output. Anything that comes out of a computer to any other device. With a GIS, output may come in the form of a printed map, screen displays, a tabular data summary, or a data file.
• overlay analysis. The process of combining spatial information from two or more maps from the same geographic area to derive a map consisting of new spatial boundaries and entities or themes.
• pan. To widen the view perspective in a graphic display (i.e., "zoom out").
• parcel. See cadastral parcel.
• pen plotter. A plotter that uses pens as drawing elements.
• pixel. Short for "picture element." The smallest discrete element which makes up a raster image. Refers also to individual grid cells in a raster.
• planimetric data. Spatial data that do not take topographic relief information into account for establishing position.
• planimetric map. A map that represents only the horizontal positions of features. It is typically used as part of a base map.
• plat. A diagram drawn to scale showing all essential data pertaining to the boundaries and subdivisions of a tract of land. It is often a legal document.
• point. A single x,y coordinate that represents a geographic feature that is too small to be displayed as a line or a polygon at a particular scale. Map examples include wells, weather stations, and navigational lights.
• polygon. A two-dimensional figure with three or more sides intersecting at a like number of points. It is defined or bounded by a closed line or arc and has attributes that describe its geographic features.
• precision. (1) The degree of discrimination with which a quantity is stated. For example, a three-digit number discriminates among 1,000 possibilities. (2) Statistical measure of repeatability, usually expressed as variance or standard deviation of repeated measurements about the mean.
• preprocessing. Preliminary processing or transformation of raw data required to facilitate further cartographic processing.
• projection (map projection). A mathematical model that transforms the locations of features on the earth's surface to locations on a two-dimensional map surface. Some map projections minimize distortion of the feature's shape; others minimize distortion of area, distance, or direction.
• projection conversion. The mathematical transformation of a map from one projection system to another. It is most often used to standardize projections when maps from two or more projection systems are integrated into a GIS.
• proximity analysis. Analytical technique used to determine the relationship between a selected point and its neighbors.
• proximity search. Analytical procedure to identify occurrences of predefined data elements in the neighborhood of a selected point or feature.
• quadrangle maps (quads). A rectangular, or nearly rectangular, area covered by a map. The outline is generally defined by latitude and longitude.
• quadtree. A hierarchical data model that provides a compact raster representation by using a variable-sized grid cell. Finer subdivisions are used in areas requiring finer detail, providing a higher level of resolution. As the map theme becomes more variable or complex, a quadtree structure is not as efficient as some other data models.
• query language. A high-level programming language, using words that closely resemble ordinary language, that provides for the easy retrieval of information.

• raster data. Cell data arranged in a regular grid pattern in which each unit (pixel or cell) in the grid is assigned an identifying value based on its characteristics.
• raster/vector conversion. To convert data from raster format to vector format with position and orientation selected by the user. Also known as a raster-to-vector conversion, or vectorization.
• rasterization. See "vector/raster conversion."
• reclassify. Procedure to change the classification of existing data.

• record. A group of logically related attribute descriptors for one feature (e.g., a house in an attribute table that contains information about houses in a community). It is commonly displayed as a row in a relational attribute table. Contrast with item.
• rectification. The process of removing the effects of tilt, relief, or other nonsystematic distortions from imagery, photographs, or maps.

• registration. Process of registering different themes to a common coordinate system or to one theme that is used as a standard so that themes can be consistently overlaid.
• relational database. A method of structuring data in the form of records so that relations between different entities and attributes can be used for data access and transformation.
• relational join. The operation of relating and physically merging two attribute tables using a common or relational item.
• relational operators. Phrases such as "greater than," "less than," "maximum," "minimum," and "contains" that are used to compare values associated with spatial data.
• remote sensing. The act of detection and/or identification of an object, series of objects, or landscape without having the sensor in direct contact with the object. Often results in the generation of image data. See also image processing.
• resampling. A process of assigning values to new, rectified, or rescaled (re-sized) cells in a raster database.
• resolution. The minimum distance between two objects that can be distinguished by a sensor. While most often it is a synonym for spatial resolution, it also applies to spectral and temporal aspects of remote sensing imaging systems.
• routing analysis. A type of network analysis that is used to optimize vehicle routing (e.g., routing of emergency services, school buses, mail delivery, municipal garbage collection).
• rubber sheeting. A procedure to stretch or shrink a subarea or portion of a map or image to fit or come into registration. This process is sometimes called warping. The warp is completed using control points.

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