GIS Dictionary

The difference in elevation between adjacent contour lines.

[cartography] A line on a map that connects points of equal elevation based on a vertical datum, usually sea level.

[data capture] Assigning elevation values to contour lines.

[remote sensing] In remote sensing and photogrammetry, the ratio between the energy emitted or reflected by an object and that emitted or reflected by its immediate surroundings.

[graphics computing] The ratio between the maximum and minimum brightness values in an image.

[graphics computing] Increasing the contrast in an image by expanding its grayscale range to the range of the display device.

[computing] A basic element of a software application’s GUI. Examples of controls include menus, buttons, tools, check boxes, slider bars, text input boxes, and combo boxes.

1 [surveying] An accurately surveyed coordinate location for a physical feature that can be identified on the ground. Control points are used in least-squares adjustments as the basis for improving … Read more

[spatial statistics use for geostatistics] In statistical testing, a set of assumptions that will be accepted by test data if the null hypothesis is rejected. In surveying, the alternative hypothesis … Read more

[cartography] The angle between a vertical line (grid north) and true north on a map.

[data conversion] The process of changing input data from one representation or format to another, such as from raster to vector, or from one file format to another, such as … Read more

[mathematics] The smallest convex polygon that encloses a group of objects, such as points. In ArcGIS, TIN boundaries are convex hulls by default.

[mathematics] A polygon in which a straight line drawn between any two points inside the polygon is completely contained within the polygon. Visually, the boundary of a convex polygon is … Read more

[ESRI software] In Survey Analyst, a process of computing a sequence of survey point locations starting from an initial known point. Each new survey point is defined by a traverse … Read more

A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or … Read more

The process of converting the coordinates in a map or image from one coordinate system to another, typically through rotation and scaling.

[astronomy] The official timekeeping system of the world’s nations since 1972. It refers local time throughout the world to time at the prime meridian, and is based on atomic clocks, … Read more

[coordinate systems] A set of values represented by the letters x, y, and optionally z or m (measure), that define a position within a spatial reference. Coordinates are used to … Read more

[statistics] An association between data or variables that change or occur together. For example, a positive correlation exists between housing costs and distance from the beach; generally, the closer a … Read more

[data models] A buffer drawn around a line.

[spatial analysis] A form of spatial analysis usually applied to environmental and land-use data in order to find the best locations for building roads, pipelines, and other linear transportation features.

1 [data analysis] A function of time, distance, or any other factor that incurs difficulty or an outlay of resources. 2 [network analysis] In ArcGIS Network Analyst, an attribute of … Read more

[spatial analysis] A raster dataset that identifies the cost of traveling through each cell in the raster. A cost raster can be used to calculate the cumulative cost of traveling … Read more

[ESRI software] The calculation of the least cumulative cost from each cell to specified source locations over a cost raster.

[ESRI software] An ArcGIS Spatial Analyst function that identifies the nearest source from each cell in a cost-weighted distance grid. Each cell is assigned to its nearest source cell, in … Read more

[ESRI software] An ArcGIS Spatial Analyst function that provides a road map from the cost weighted distance grid, identifying the route to take from any cell, along the least-cost path, … Read more

[ESRI software] An ArcGIS Spatial Analyst function that uses a cost grid to assign a valuethe least accumulative cost of getting back to the sourceto each cell of an output … Read more

[software] Acronym for commercial off-the-shelf. Commercially available software or systems that are ready to use and which do not require significant customization.

[federal government] The primary legal subdivision of all U.S. states except Alaska and Louisiana. The U.S. Census Bureau uses counties or equivalent entities (boroughs in Alaska, parishes in Louisiana, the … Read more

[federal government] A statistical division of a county recognized by the U.S. Census Bureau for data presentation. County subdivisions can include census county divisions, census subareas, minor civil divisions, and … Read more

[statistics] A statistical measure of the linear relationship between two variables. Covariance measures the degree to which two variables move together relative to their individual mean returns.

[ESRI software] A data model for storing geographic features. A coverage stores a set of thematically associated data considered to be a unit. It usually represents a single layer, such … Read more

In ArcInfo, a classification describing the format of geographic features and supporting data in a coverage. Feature classes include point, arc, node, route, route system, section, polygon, and region. One … Read more

[coordinate systems] The units of the coordinate system in which a coverage is stored (for example, feet, meters, inches).