S
SAIF
Spatial Archive and Interchange Format. SAIF is the Canadian draft National Standard for Geomantic Data Interchange. Designed originally by the Government of British Columbia, it is a specification for data, which includes an object oriented data model and a language for describing both spatial and non spatial data.
samples
Groups of cells in an image selected to represent one feature type or land cover of interest. You define samples from your knowledge of the site. (See also: prototypes, training sets.)
sample set
For unsupervised classification processes, a set of sample cells that is selected from the input raster set and used to automatically define classes. The selection of the sample set during processing is controlled by a sampling interval (in line and column directions).
sampling
The process of approximating an image using a subselection of pixels. Sampling is usually done at constant intervals though this is not required. Generally, as the number of samples increases, the quality of the image increases. (See also: resample.)
SAN
System network architecture. Networking protocol popular in IBM environments.
SAR
Synthetic Aperture Radar.
sash
A small graphic control component on the separator between two panes. A sash moves the separator to change the size of the panes. Drag the sash with the mouse to make a pane larger or smaller.
Satellite Image
A picture of the earth taken from an earth orbital satellite. Satellite images may be produced photographically or by on-board scanner (eg MSS)
saturation
One of the three coordinates that the HBS and HIS color domains use to define a display color. Saturation designates how far away a color is from a gray or neutral color of equal intensity. (See also: HBS, HIS.)
scalar
An SML variable for numeric values. The SML naming conventions presume any variable that begins with a lower case letter is a scalar value or a string.
scale value
A number used as a multiplier to translate a set of numbers from one range of values into another. For example, a set of decimal values that range between 0 and 2 could be projected into the numeric range of 0 to 100 by multiplying each number in the set by a scale value of 50.
scanner
A digitizer that produces an image (raster object) from flat input material such as photographs, maps, and drawings.
SCIAMACHY
SCIAMACHY is a spectrometer that maps the air over a very wide wavelength range, which allows detection of trace gases, ozone and related gases, clouds and dust particles throughout the atmosphere. It works by measuring sunlight, transmitted, reflected and scattered by the earth's atmosphere or surface in the ultraviolet, visible and near infrared wavelength region. With a 960-km swath it covers the entire world every six days. John Burrows of the University of Bremen's Institute of Environmental Physics first devised the idea for SCIAMACHY, and he now serves as its Principal Investigator. SCIAMACHY is part of a family of atmospheric spectrometers that also includes GOME on ERS-2 and the forthcoming GOME-2 instrument launching next year with the first MetOp mission
scroll
"To move the current text or image up, down, or across the monitor so that new text or image appears on one edge of the screen as it disappears from the other" (Random House). Scrolling is controlled with the mouse and the arrow keys. For example, a list of objects in a project file which is too long to fit on the text screen can be scrolled up and down with the vertical arrow keys.
scroll bar
Indicates position of current view in relation to the whole, and used to change the user's viewpoint. The scroll bar consists of a slider, scroll area ("trough"), and scroll arrows.
SCS
Soil Conservation Service. A service of the United States Department of Agriculture.
SCSI port
Small Computer Systems Interface (SCSI is pronounced "skuzzy.") A physical connection between a computer and a peripheral device, such as an external hard drive or optical drive.
seam
The junction in the area of overlap between raster objects combined by tiling or mosaicking.
SECAM
Sequential Couleur à Memoire. A video standard used in France and the former USSR.
sections of land
The U.S. Public Land System divided much of the U.S. into square sections of land with an area of approximately
square mile (sides 1 mile long). Since most of this survey was completed in the late 1800s, these sections vary greatly in area and shape. In some areas survey adjustments have created sections as big as
square miles. Sections are the basic unit of land ownership in the central and western U.S. They are usually bounded by roads that give rise to the checkerboard land patterns characteristic of these areas.
seed point
The seed point for a watershed is the lowest point in a watershed, or the point to which all other points drain. The seed point for a flow path is the highest point of the path. Water flows from there to a watershed seed point or the boundary of the study area.
segment
A segment is a line or polygon that forms part or all of a glyph. A glyph made from polygons will be filled when printed but may optionally be displayed in outline form to increase display speed. A glyph made of line segments rather than polygons is known as a stroke font. It is faster for the computer to draw a stroke font than a font made of polygons. The ability to create stroke fonts in the Outline Font Editor is not yet implemented.
select
To mark one or more of a group of elements in preparation for acting upon them by some program operation such as move, copy, edit, open, analyze, display, or delete.
select button
The mouse button used to make a selection.
selection box
(more properly called the location box) A graphical symbol that marks the current location of keyboard focus for an operation. Moved with Tab and arrow keys.
selection highlight
An item displayed in reverse video in a text list, that indicates which member of the list is selected. You complete the selection by pressing the <Enter> key (or double clicking with the left mouse button).
selection query
(in database queries) A selection query is constructed from one or more comparison expressions. Only if the entire query evaluates to "true" (non-zero) for an element, is the element included.
selection set
All elements currently selected by the Element Selection tool for viewing or editing make up the selection set. One element in the selection set, generally the last element selected, is the active element. Attribute assignments and editing changes can be applied to just the active element or to all elements in the selection set. (See also active element.)
separator
A dividing line that marks a logical division between areas of a window or menu.
serial port
A physical connection between a computer and a peripheral device, such as a plotter. A serial port uses a connection that has at least three wires. (The standard IBM AT serial port uses nine wires.) The eight bits in a byte are transmitted serially, or end to end, through a single line while the remaining lines contain status information such as "send me more" and "stop sending." DOS currently allows the use of two different standard serial ports named COM1 and COM2.
shaded relief
See - relief
shear
Angular slant given to a vector font to produce the effect of italics.
shift sequence
A keyboard technique for text entry in a language that uses more than one character set, such as Japanese which uses a mix of ideographs, Latin characters, and Japanese phonetic characters. The user enters a shift sequence to indicate a switch from one character encoding scheme to another. Electronically, each character is preceded by a shift sequence byte that identifies its character set.
SIF
Standard Interchage Format, a spatial data exchange format. A standard or neutral format used to move graphics files between computer systems.
slider
A graphic control component that controls the setting of a variable. Move the slider by dragging it with the mouse to make its associated value larger or smaller.
Sliver
A gap formed when two lines which should be continuous are slightly separated in a graphical representation or map.
Slivers polygon
A small area feature commonly occurring along the borders of polygons following the topological overlay of two or more coverages.
slope
A measure of how steeply a surface or line inclines. Slope is computed by dividing a line's vertical rise or fall by the distance the line travels on the surface (the "rise over the run") - usually expressed as a percent.
smart line following
An interactive process for converting raster line images to line elements in a vector object. The user clicks on a line image, and the process follows the line, over-tracing a vector line. The process stops at the edge of the raster, at the end of the line, or at a spaghetti junction of lines that the user must guide it across.
SML
Spatial Manipulation Language. A programming language for manipulation of raster, vector, and CAD objects provided by the Map and Image Processing System. SML allows you to enter either immediate commands or to write a full program. To use SML interactively, you enter single commands from the keyboard and SML executes each command as it is entered. To use structured programs with SML, you prepare a program file ahead of time.
soil association
A soil mapping unit containing adjacent soils, but the survey did not take the time and effort to delineate them. Soil association information is suitable for general planning only: to compare areas, to locate refuge tracts, and certain kinds of land use.
soil complex
A soil mapping unit with two or more soils so intricately mixed that they cannot be shown separately on the map.
soil group
(undifferentiated) A soil mapping unit with two or more soils. For the purposes of the map, there was little value in separating them.
soil mapping unit
An area on a soil map with a complete, closed border drawn by a soil scientist, usually representing an area of one type of soil. A mapping unit is nearly equivalent to a soil phase with the exception of small scattered bits of other soils that are not worth showing.
soil phase
A subset of a soil series differentiated by slope, stoniness, or other characteristics that affect the soil's usefulness.
soil profile
The sequence of natural layers, or horizons, in a soil. A profile extends from the surface down into the parent material that has not been changed much by leaching or by the action of plant roots.
soil series
A U.S. category of soil classification including soils that have similar profiles (thickness, arrangement) named for a town or geographic feature near its first observation. Soils in a series are essentially alike in characteristics that affect their behavior in an undisturbed landscape.
solid modeling
The process of rendering a 3D surface from vector type data. This process is widely used in CAD software packages to prepare a realistic color presentation of a component part, a building, or other solid object from complex vector-oriented engineering drawings. In GIS vector-oriented software, contours of the surface of the land stored as vectors might be used to render a solid model of the land's surface.
spaghetti digitizing
Entering line data in no particular order using a digitizer.
SPANS
The SPatial ANalysis System from TYDAC Technologies.
spatial
An adjective applied to objects that vary in space in two or three dimensions.
Spatial Manipulation Language
See - SML
spectral band or spectral region
A well-defined, continuous wavelength range in the spectrum of reflected or radiated electromagnetic energy. Red, green, and blue are all spectral regions within the portion of the spectrum that is visible to humans as light. Color-infrared images are composed of red, green, and a spectral region commonly called the photoinfrared, which is not in the visible portion of the electromagnetic spectrum. (See also: color-infrared, electromagnetic spectrum.)
spheroid
Any shape that closely resembles or approximates a perfect sphere. In the context of map projections, a spheroid is an ellipsoid of rotation that is flattened at the poles, like the earth.
spline
An interpolating polynomial for a set of coordinate points used to fit a curve that connects the points. (See also: Bézier curve)
SPOT
The French Systeme Probatoire d'Observation de la Terre. There are two SPOT satellites: one collects images with 10-meter ground resolution in a single panchromatic spectral region; the other collects 20-meter images in the three spectral regions used for color-infrared maps. SPOT satellites may be pointed at an angle off-axis or off-nadir to collect forward and rearward images: a technique that yields stereoscopic image pairs from which accurate elevation rasters can be computed.
spread
The spread operation changes the colors between two selected tiles in the Color Map Editor window.
spur
A false line segment that extends a short distance beyond a T-junction of two lines. Binary raster thinning processes often leave spurs that should be erased by raster editing before final vectorization.
SQL
Structured Query Language. A Syntax for defining and manipulating data from a relation database. Developed by IBM in 1970 s, it has become an industry standard for query languages in most relational database management system.
SRG
Standardized raster graphic, a digital representation of a map or chart which is captured by automatic digitization (scanning), stored on a digital storge media and displayed on a raster screen or raster plotter, obtained by a regular scan of a paper map or chart or repromat. It consists of a raster data set of RGB intensities or colour (SIC) coded.
stack
A hierarchical arrangement of images and other information used by HyperIndex that graphically links logically related objects or files. A stack has the inverted tree form of a genealogy chart. (See also: HyperIndex, link.)
standard parallel
A parallel of latitude used as a control line in the computation of a map projection, and which is therefore, true to scale. Some map projections have no defined standard parallel, others have one, while others have two.
standard 64 annotation colors
In 8-bit contexts the Color Map Editor window normally reserves the first 64 colors for a standard set of user annotation colors for text and overlays. That leaves 192 colors for the image itself - ample color space for representing most natural color images to the human eye. The 64 standard colors are chosen at fixed intervals in the RGB color model. They generally appear brighter and purer than the subdued natural tones of the underlying image.
State Plane Coordinate System or SPCS
The State Plane Coordinate System (SPCS) defines map coordinates by zone for the United States. Each zone has one central meridian and scale factor, which permits all USGS quadrangle maps in a zone to be mosaicked exactly. Zones with north-south extent use the Transverse Mercator projection, while those with east-west extent use Lambert Conformal Conic. (The panhandle of Alaska is the only exception, and uses Oblique Mercator).
stepwise linear classification
A supervised image processing routine applied in the same fashion as maximum likelihood classification using training sets, or prototypes. This method applies the classical techniques of stepwise linear discriminant analysis to set up the classification model and map the materials desired from the input raster objects. (See also: maximum likelihood classification)
stereo elevation
An elevation surface derived from stereo pairs of remote sensing imagery. For example the SPOT satellite can collect an "off nadir" image and then in a subsequent fly-over collect its counterpart to make a stereo pair. The stereo elevation process takes the 3D effect of that stereo pair to derive an accurate raster object of elevation values.
style query
(in database queries) A style query is constructed from a combination of comparison expressions, which examine values of element and database variables, and assignment statements, which set the values of drawing variables.
subtractive color
Creating color by using absorption or scattering to selectively remove some of the colors of light, or radiation, reaching the human eye is a subtractive process. The use of pigments, such as color printing or a painting, demonstrate this subtractive color process. The greater the number of different colored pigments mixed together, the darker a pigmented object appears. This darkness results from an increased absorption of visible light by the pigments and, consequently, less light reflected to the eye. The presence of fewer pigments or their absence altogether results in greater reflectance of visible light. Selective absorption removes a color(s) from the reflected radiation and results in the perception of the complementary color.
subwindow
An auxiliary window that opens as the result of some user action in the parent window (such as pressing a button), or of some processing condition (a dialog box subwindow might open with a message or warning.)
Suits-Wagner classification
A simple form of supervised or semiautomatic classification that operates similarly to a boxcar or parallelepiped classification. This method defines the sides of the box for each class as plus and minus one standard deviation from the mean of the values of the prototype, or sample, values selected to represent that class. This method has the advantage that like a simple boxcar classifier, it is very fast to apply the resulting decision rule to the unknown pixel values. More information on this process can be found in: H.L. Wagner and G.H. Suits (1980) Proceedings of the 14th International Symposium on Remote Sensing of the Environment, vol. III pp. 1525-1529. Environmental Research Institute of Michigan, Ann Arbor Michigan. A Low Cost Classification Algorithm for Developing Countries.
supervised classification
A type of automatic multi-spectral image interpretation in which the user supervises feature classification by setting up prototypes (collections of sample points) for each feature, class, or land cover to be mapped.
surface fitting
Techniques that use 3-dimensional vector point data to create a raster object containing an elevation surface. Various methods can be used to fill the gaps between the vector points and derive the elevation values for the intermediate raster cells.
SVHS video
Super VHS video. A newer video standard for cameras and recorders. SVHS equipment achieves a higher resolution than conventional VHS equipment. SVHS overcomes some of the VHS band width limitations by maintaining the video in two separate components and signals.
symbol overlay
A vector object can have symbol shapes assigned to some or all of its point features. When this vector object is displayed over (or overlaid on) an image, you can also choose to display the symbols over the top of the features in the underlying image. Such symbols may also be attached to database records and used to graphically retrieve such reference information. For example, a symbol overlay that uses ducks to represent nesting sites could be shown over a habitat map. A click on a particular duck symbol could retrieve a record from an associated database and display it on the text screen to provide such information as the date of first occupancy, number of eggs, number of fledglings, and so on. (See also: overlay.)
symmetric minima
A raster cell that has a value less than two opposite neighbors in any direction. A raster object of symmetric minima is calculated from an elevation raster object and provides a representation of the relative roughness of terrain.
synthetic resolution
An apparent increase in spatial resolution achieved either by resampling image rasters or by combining images from different sensors of varying resolutions (such as SPOT panchromatic and TM multispectral).
nts or their absence altogether results in greater reflectance of visible light. Selective absorption removes a color(s) from the reflected radiation and results in the perception of the complementary color.
subwindow
An auxiliary window that opens as the result of some user action in the parent window (such as pressing a button), or of some processing condition (a dialog box subwindow might open with a message or warning.)
Suits-Wagner classification
A simple form of supervised or semiautomatic classification that operates similarly to a boxcar or parallelepiped classification. This method defines the sides of the box for each class as plus and minus one standard deviation from the mean of the values of the prototype, or sample, values selected to represent that class. This method has the advantage that like a simple boxcar classifier, it is very fast to apply the resulting decision rule to the unknown pixel values. More information on this process can be found in: H.L. Wagner and G.H. Suits (1980) Proceedings of the 14th International Symposium on Remote Sensing of the Environment, vol. III pp. 1525-1529. Environmental Research Institute of Michigan, Ann Arbor Michigan. A Low Cost Classification Algorithm for Developing Countries.
supervised classification
A type of automatic multi-spectral image interpretation in which the user supervises feature classification by setting up prototypes (collections of sample points) for each feature, class, or land cover to be mapped.
surface fitting
Techniques that use 3-dimensional vector point data to create a raster object containing an elevation surface. Various methods can be used to fill the gaps between the vector points and derive the elevation values for the intermediate raster cells.
SVHS video
Super VHS video. A newer video standard for cameras and recorders. SVHS equipment achieves a higher resolution than conventional VHS equipment. SVHS overcomes some of the VHS band width limitations by maintaining the video in two separate components and signals.
symbol overlay
A vector object can have symbol shapes assigned to some or all of its point features. When this vector object is displayed over (or overlaid on) an image, you can also choose to display the symbols over the top of the features in the underlying image. Such symbols may also be attached to database records and used to graphically retrieve such reference information. For example, a symbol overlay that uses ducks to represent nesting sites could be shown over a habitat map. A click on a particular duck symbol could retrieve a record from an associated database and display it on the text screen to provide such information as the date of first occupancy, number of eggs, number of fledglings, and so on. (See also: overlay.)
symmetric minima
A raster cell that has a value less than two opposite neighbors in any direction. A raster object of symmetric minima is calculated from an elevation raster object and provides a representation of the relative roughness of terrain.
synthetic resolution
An apparent increase in spatial resolution achieved either by resampling image rasters or by combining images from different sensors of varying resolutions (such as SPOT panchromatic and TM multispectral).