Saturday, July 25, 2015

Important terms used in GIS

ABSOLUTE ACCURACY:
It is a measure of the difference between the location of the object as specified in a GIS and its true location in the real world

ADAPTIVE SAMPLING:
It is a data sampling technique that uses accumulated knowledge from samples already taken to direct future sampling. Ex: Redundant sample points may be rejected during the sampling process on the grounds that they carry too leittle extra information

ADDRESS GEOCODING:
It refers to the process of alphanumeric locational identifiers to spatially related information. The process implies a geographic base file which can be used to pass addresses in order to determine characteristics about the geometry.

ALBEDO:
The ratio of light reflected by a planet or satellite to that received by it.

ALIASING:
The appearance of jagged lines on a raster display

ANTI-ALIASING:
Anti-aliasing removes or greatly smoothes the jagged, stair-step appearance of a digital line by filling-in some of the intermediate and flanking cells in lower-intensity colors.

Arc:
A portion of the perimeter of a two dimensional closed figure lying between two nodes at which two or more arcs intersect. An arc usually represents a common boundary between two adjoining mapping units.

ARC SECOND:
The SIXTIETH part of of a minute of angular measuere represented by "

AREA:
A level of spatial measurement referring to a two dimensional defined space.

ASPECT:
It refers to the compass direction (usually from North) of the line of steepest slope at some selected point.

ASPECT RATIO:
It refers to the ratio of horizontal scale to vertical scale for printing or display

ATTRIBUTE:
It refers to the set or collection of data that describe the characteristics of real world entities or conditions

ATTRIBUTE QUERY:
It is the process of selecting data items from a file based system, based on values of specific attributes or combinations thereof defined by arithmetic, relational and logical expressions

AUDIT TABLE:
In a GIS, a table of information describing a maps subjects, items, perimeters and areas.

AUTOCORRELATION:
It refers to the statistical concepts expressing the degree to which one value of an attribute covaries with other values of the same attribute. Especially in the spatial case, it refers to the degree to which the values of an attribute of two objects covary with the distance separating them.
Mathematical autocorrelation techniques can be applied to overlapping image segments in processes such as mosaicking and raster-to-vector registration. Ex: Autocorrelation can automatically find the best seam between overlapping image segments.

AUTOMATED CARTOGRAPHY:
It is the process of drawing maps using computer driven display devices such as plotters and graphic screens.

AVHRR IMAGERY:
Advanced Very High Resolution Radiometer Imagery produced by NOAA satellites

AVIRIS IMAGERY:
Airborne Visible Infra-Red Imaging Spectrometer imagery. These are multispectral images of approximately 240 coregistered spectral bands collected by NASA aircraft.

AZIMUTH:
The angle defined by the intersection of a map's central line of projection with any meridian. If a map projection uses a central line that is oriented to the TRUE NORTH, such as a standard meridian, the azimuth is 'ZERO'.

AZIMUTHAL PROJECTION:
It is a class of map projections in which the directions of all lines radiating from a central point are the same as the directions of corresponding lines on the sphere. Azimuthal projections are formed onto a plane which is usually tangent to the globe at a pole (polar projection), at a point on the equator or any selected intermediate point. Most azimuthat maps do not have standard parallels or standard meridians. Each map has only one standard point, "THE CENTER".
*Azimuthals are suitable for minimizing distortion in a circular region such as antarctica BUT NOT for an area with a predominant length in on direction*

BAND OR SPECTRAL BAND:
A range of wavelength of electromagnetic radiation.

BASE DATA:
It is the base level of map data on which other information is placed for purposed of comparison or graphical correlation. Map data that RARELY CHANGES and is USED  REPEATEDLY is called base data.

BEARING:
It is the horizontal angle of a direction, measured in the quadrant of the line as degrees East or West.
Ex: NE = 45 degrees East of North; SW = 45 degrees West of South

CADASTRAL LAYER:
A set of information depicting the pattern of land ownership rights in an area.

CARDINAL DIRECTION:
The four principal directions: North, East, West and South.

CARTESIAN COORDINATES:
A coordinate system in which location of points in space is expressed by reference to three perpendicular axes (x,y,z)

CARTOGRAPHY:
The art or science of making maps

CELL:
One value in a raster that corresponds to a specific area on the ground

CENTRAL MERIDIAN:
The North-South meridian of a map projection around which the map is centered.

CHANGE IMAGE:
An image produced using raster algebra that shows change over time between coregistered images. (Multitemporal image processing)
Ex: Subtracting old raster image from New raster object could show the difference between early season crop development and mid-season development or between pond surface area from year to year.

CHOROPLETH MAP:
A map with areas coloured or shaded such that the darkness or lighness of an area symbol is proportional to the density of the mapped phenomenon. It is a map of uniform values separated by abrupt boundaries. ADJACENT AREAS ARE NOT NECESSARILY CLOSE IN VALUE.

CIR IMAGE:
Colour Infra Red Image. These images are collected by an electron scanner or a camera that uses a special film with sensitivity from green through infrared. Photographic infrared radiation just beyond the range of human vision is displayed as red. Normal red from the scene becomes green and green becomes blue. Normal blue is filtered out and not recorded.
CIR images are used to show vigor of plant life. Healthy vegetation appears red while distressed or damaged vegetation appears pink, tan or yellow.

CLUMP:
It represents a set of contiguous line, node and polygon elements in a vector object

CLUSTERING:
It is a process in which multiple, spatially coincident, coregistered raster objects are reduced to a single raste object called a cluster map.

CMY:
Cyan-Magenta-Yellow

COGO:
Coordinate Geometry. A set of mathematical tools and functions for encoding and converting bearings, distances, angles etc into coordinate information. Data is input and the geometry is determined automatically.

COMPLEX CORRELATION:
It is the ability to compare maps representing different time periods, extracting time differences, or computing indices of change. It is a multitemporal analysis function.

COMPLEX GENERALIZATION:
It refers to generalization that may require change in the type of an object or relocation in response to cartographic rules.

COMPOSITE MAPS:
It refers to a single map created by joining together several separately digitized or scanned maps.

COMPRESSION:
It is a method for reducing the file size usually using a run-length coding algorithm

CONDITIONAL MAP ELEMENT:
It refers to a piece of map upon which society places conditions. Ex: Land use, Zoning, Historic district etc.

CONNECTIVITY ANALYSIS:
It is the ability to identify areas or points that are not connected to other areas or points by linear features.

CONTIGUITY ANALYSIS:
It refers to the adjacency relationships between any given polygon and its neighbours. This involves summarizing and relating attributes of neighbouring polygons to the polygon being examined.

CONTINUOUS DATA:
Data in a raster object is said to be continuous if it can be represented by a three dimensional surface such that intermediate values can be derived with meaningful results.

CONTOUR (N):
It is an imaginary line on the ground, all points of which are at the same elevation above or below a specific datum (M.S.L.)

CONTOUR (V):
It refers to interpolation of elevation of points at specific intervals when elevations of a set of regularly or irregularly spaced points is given.

CONTOUR MAP:
It is a topographic map that uses contour lines to portray relief . Contour lines join points of equal elevation.

CONTROL POINT:
Points and or cells which are used to establish map coordinate control for uncalibrated objects. In the manual mosaic process, a control point is a feature in a piece of the mosaic for which the map coordinates are known. In the raster-to-vector calibration process, a control point is a feature that is co-located between the uncalibrated raster object and the calibrated vector overlay. A control point shows on both a raster object and an overlaying vector object.