D
DAL
Data Access Language. Apple's former standard to allow applications to communicate with relational databases. DAL is middleware on a network. It is a program installed on the database surver to provided common SQL access for all database servers on a network. Apple has licensed this technology to Independence Technology Inc.
data access security
Measures taken to control system users ability to view or modify data. these measures can include logical views of data and explicit access rights by group or individual users.
database
A logical collection of inter related information, managed and stored as a unit, usually on some form of mass storage system such as magnetic tape or disk. A GIS database includes data about the Spatial locations and shape of geographic features recorded as points, lines, pixels, grid cells or tins as well as their attributes.
database design
The formal process of analysing facts about the ral world onto a structured database model. Database design is characterised by the following phases: requiremental analysis, logical design and physical design.
database form
A database form allows you to reorganize the information in a table for display in single record view. This reorganization may include changing the order and placement of fields and / or displaying only selected fields from an existing database table. You can also modify field titles to include spaces, which are not allowed in actual field names, to exceed the 15 character maximum, or you can change the name entirely if the original seems too cryptic for the intended audience. You can also add text that is not associated with a particular field to provide logical groupings for the information presented in the form. A database form cannot exist without an accompanying database table. Editing in the default table layout or in any of the forms created as an alternate means of viewing the same information alters the single set of values used in all cases. Database forms are stored as subobjects of the database.
DATABASE INTEGRATOR (DBI)
ARC/INFO Software's link to relational database Management Systems (RDBMS) DBI enables ARC/INFO users to access existing commercial databases and take advantage of the power and capabilities of RDBMS.
database object or dBASE object
A database is a collection of information related by some unifying theme, such as demographics, epidemiology, or geographic location. There are a number of popular database programs, such as dBASE IV, that assist in the retrieval and management of such information in electronic form.
database query
The database tables attached to vector/CAD objects can be queried to reveal those elements that meet the criteria specified in the query and drawing styles can be assigned in accordance with query results. Database query can be used to select vector/CAD elements for display and assign their drawing styles.
data mask
A processing barrier that only allows data values in a chosen range to pass. You might choose a data mask to block all values outside a selected color range, eliminating all image features except those of the color you want to use in a process. You can also use a mask to select a processing area from a larger scene. The mask blocks off the parts that you want to exclude from the current analysis.
dataTip
A DataTip contains a raster cell value or element information for vector, CAD, or TIN object. For all objects except raster objects, you can designate the database table for use as a DataTip. Place the cursor on the cell or element for which you want to see a DataTip and wait briefly. DataTips operate in a manner similar to ToolTips. The DataTip and the pertinent value or information appears adjacent to the cell or element.
data type
The characteristics of columns and variables that defined what types of data values they can store. Examples include character, floating point and integer.
datum
A set of parameters and control points used to accurately define the three dimensional shape of the earth [eg. as a spheroid]. The datum is the basis of planar co-ordinate system. For eg. the North American Datum for 1983 (NAD83) is the datum for map projections and coordinates within the united states and throughout North America.
DBMS
Database Management Systems. It is a set of computer programs for organising the information in a database. Typically, a DBMS contains routines for data input, verification.
DCW
"Digital Chart of the world". The first 1:1000,000 scale digital base map of the world. The DCW contains topologically based vector datadigitised from the US Defence Mapping Agency's Operational Navigation charts.
DDL
Data definition language. SQL statements that can be used eithier interactively or within programming language source code to define databases and their components.
defaults
The start-up settings for a system or an individual process. Well thought out defaults are one of the simplest and most easily incorporated forms of artificial intelligence that can exist in a system.
degree or °
A unit of measurement equal to 1/360 of a circle. A degree of latitude on the earth's surface is about 69 miles. A degree of longitude is about 69 miles at the equator and undefined at the poles, but any point on the surface rotates through a degree of longitude in about 4 minutes of time. (See also: arcsecond, minute.)
Delaunay criterion
The technique used to generate the TIN object, known as Delaunay triangulation, produces a set of triangles that are as equi-angular as possible. All circumcircles of Delaunay triangles contain no points other than the three that define the triangle and its circumference. Satisfying the Delaunay criterion ensures that any point on the surface is as close as possible to one of the nodes, the number of long skinny triangles is minimized, each sample point is connected with two nearest neighbors to form a triangle, the triangulation solution is unique and independent of the order in which the points are processed, and the solution produced allows easy generation of Voronoi diagrams (Thiessen polygons) for the same set of input points. Voronoi diagrams are widely used in spatial analysis.
DEM
1. Digital Elevation Model. (Also DTM, "Digital Terrain Model"). A computerized representation of an elevation surface. Specifically, a raster in which the value in each cell represents the surface elevation at that location in the scene. DEMs are USGS geographic elevation data distributed in raster form on open reel magnetic tapes. There are 2 basic types: 1) The DMA type created by the Defense Mapping Agency in both a fixed cell size and a 3 x 3 arcsecond cell size distributed in 1 x 1 degree files. 2) A newer format for those 7.5' USGS quadrangles that have been processed into 1 x 1 arcsecond elevation cells.
2. A digital representation of a continious variable over a two diminution surface by a regular array of Z valuies referened to a common datum. Digital elevation madels are typically used to represent tereain relief. Also refered to as digital terrain model (DTM)
3. An elevation Database for elevation data by map sheet from the National Mapping Division of the U.S. geological survey (USBS).
4. The format of Ditital elevation data sets.
DEM Extraction
A step in Stereoscopic Modeling process. DEM Extraction uses the resampled epipolar LEFT and RIGHT images created by the Prospective Projection step, and creates an output elevation raster object of the selected model area.
dendrogram
A tree diagram whose branches depict a hierarchical classification structure, showing the degree of relatedness of different classes.
Densify
The process of adding vertices to an arc at specified distances, without changing the arc's shape.
depressionless elevation
(watershed analysis) A version of the elevation surface that has all depressions (puddles, ponds, and potholes) filled.
depressionless raster
An elevation raster created from the original or from processed elevation rasters with all depressions filled. Each depression filled raster becomes the current input raster for further processing. The final depressionless raster is attained when the number of depressions is reduced to zero.
Desceiptive data
Tabular data deceibing the characteristics of geographical features. Can include numbers text, images and CAD deawings about features. ARC/INFO. Stores deceiptive data in feature atteibuts tables and in related tables.
Destination
In spatial interaction, the location of the end of a teip. For a shop or an office, where a consumes or working is going Destination are represnted as center in a network coverage, as points in a point coverage and as lable point in a polygon coverage.
developable surface
A geometric form capable of being flattened without stretching or tearing, such as cylinder or a cone (both of which can be cut and laid out flat), and a plane (which is already a flat surface).
device independent
Not constrained by idiosyncrasies of hardware environment. Device independent software is also designed so that all of its procedures look and work the same way across a variety of hardware configurations.
DGIS
Direct Graphics Interface Standard.
DGM
Digital Geospatial Metadata. DGM was approved in June 1994 by the Federal Geogrophic Data Connistce (FGDC) DGM describes the specifications for the content, quea lity, conditions and other characteristics of metadata. (data aboutable). The standard provides a common set of terminology and definitions for documentation of Geospatial data. DGM establishes the names of data elements to be used for the data elements to be used for these purposes, definition of these data elements and groups and information about the values that are to be provide for the data elements.
diacritic
An accent mark added to a character to distinguish it in pronunciation or meaning from other uses of the same character. Common diacritics, for example, distinguish several versions of the Latin character "a:" á, à, â, ä, ã, and å.
dialog box
A type of subwindow that opens to display a message, warning, processing message or application components that require the user's input. The user must typically make some kind of decision and exit the dialog box before continuing with the process by pressing a button such as OK, Cancel, or Skip.
diapir
An upfolded geologic structure, such as an anticline, in which mobile, plastic core material has broken through or pierced the more brittle overlying rock.
DIGEST
The Digital Geographic Information Exchange Standard is produced under outhority of NATO's Digital Geographic Information, working Group. DIGEST is a standard for digital geographic information which will enable interoperability and compatibility among national and multinational systems and uses. DIGEST is composed of standards for two digital geographic formats: ARC Standards Raster Graphic (ASRG) and vector relational format (VRF). ASRG is limilae to ADRG and can be imported into ARC/INFO as an ADRG file with the ADRG GRID command. The ARC/Info VPFIMPORT and VIP Export convertora will process the VRF data.
digital
1. Information stored and processed with numerical digits, often in base 2. Digital information processing is constrained by the finite set of numbers a system uses, such that every data value is forced into its nearest representation. For example, a digital clock may only show hours, minutes and seconds, but not fractions of a second. At some point, every digital system faces the same kind of limit in accuracy. On the other hand, digital information is easy to copy, store, manipulate and reproduce dependably. (See also: analog.)
2. The ability to represent data in discreet, quartered units or digits.
digitize
Convert analog data into a digital form; also, more specifically, use an X-Y digitizing tablet to convert data to digital form.
digitizer
1. A device that converts an analog signal or representation to a digital one. (See also: scanner, video digitizing board, X-Y digitizer.)
2. A device for entering the spatial coordinates of mapped features from a map or document to the computer.
digraphia
Use of two different scripts for the same language, such as Latin and Cyrillic for Serbo-Croatian, Devanagari and Arabic for Hindi-Urdu, and Pinyin and characters for Chinese.
dimensionality
The number of coregistered images in a project file for one site. An image contained in one color composite raster has a dimensionality of one. An image contained in a three-raster RGB set has a dimensionality of three. A Landsat TM image map for a single date will have a dimensionality of up to seven.
If elevation rasters, panchromatic rasters, and multi-date airphotos are added to the project file, the user will likely want to reduce the dimensionality of the image to simplify analysis and manipulation. (See also: dimensional reduction)
dimensional reduction
Reducing the number of coregistered rasters in a project file to speed up their analysis.
dimmed selection
A menu selection that is not currently available as indicated by its grayed-out appearance.
directory or sub-directory
In DOS, a directory is a logical, user-defined division of a storage device. For example, a user may divide a hard disk into several directories, with each directory used to store files that pertain to a certain task. One directory may contain programs and documents for word processing, another for spreadsheet analysis, and another for database manipulation.
discrete data
Geographic features containing boundaries: Point, line or area boundaries.
discrete values
Cell values of rasters that represent discrete data, such as categorical data, for which interpolated values have no meaning.
disk drive
A mechanical component of a computer that allows data to be read from or written to a spinning magnetic or optical disk.
displacement
The difference between the apparent x,y position of a feature in a raw photo and the feature's true position. Displacement is caused by camera characteristics, tilt, nearness to the target scene, and variations in the elevation of the target terrain.
display board or display card
An electronic circuit board installed in a microcomputer that translates the computer's display data into signals for the monitor.
display driver
The system module that prepares image data for a particular manufacturer's display board.
display histogram
A graph showing the number of times a data value occurs in a raster display plotted against the range of possible values. For any RGB color the user selects, the display histogram shows how may cells there are in the display for each intensity level of that color.
dissolve
The process of removing boundaries between adjacent polygons that have the same values for a specified attribute.
distance-decay functions
The spatial interoction the metha matical representation of the effect of distance on the accessibility and numbers of interaction between locations. It can be either a power or on exponential function.
distance raster
An output raster created by certain classification methods which records the Euclidean distance between each cell and its assigned class center. Distances are represented as 32-bit floating point numbers. High distance values may identify cells which were not adequately classified using the chosen method and input parameters.
dithered raster
A printer-ready 4-bit raster object in which each cell corresponds to one dot (printel) on the hardcopy output from the printer.
DLG
Digital Line Graph. A USGS map format usually used to distribute topographic maps in vector form.
DMA
Defense Mapping Agency of the US Department of Defense.
Direct Memory Access.
DML
Data Manipulation language SQL statements that can be used either interactively or within programming lauguage source code to access and retrive data stored in a database management system.
DOS
Disk Operating System. DOS for personal computers is developed and marketed by IBM and Microsoft. It provides management utilities for the files and other resources of the microcomputer.
dpi
Dots Per Inch. A measure of scanner, screen, and printing resolution. The more dots per inch, the more detail a device can process for a given area of page or display. On the other hand, the more dots per inch, the higher the demands on machine storage and processing (files get large and processing slows down).
drag
To press and hold a mouse button while moving the mouse.
drag bar
A window's title bar.
drape
A perspective or panorancic rendering of two-dimensional features superimepased an a surface.
drawing order
The order in which layers are drawn during display. The object that is first in the drawing order will appear to be on the bottom when all layers are displayed. The order of objects in the layer list reflects the displayed appearance for a group with the background always at the bottom of the list.
drawing style
The style used to render a screen or hardcopy representation of a vector or CAD element. The drawing style for point features includes size and whether unfilled, filled, or represented by a symbol. The drawing style for line elements includes line width and whether drawn in solid color or using a line pattern. The drawing style for polygon elements includes the border color and whether or not a polygon is filled. Your choice of single color filling or use of a transparent fill pattern and whether to draw the border if filled are also part of the drawing style.
driver
A set of computer commands that control some input or output process for a particular type of hardware. Usually, drivers are written in assembly language. They tend to be small, very efficient translators of general program features into the specific communication protocol required by a particular manufacturer's device. Everyone using word processing software should be familiar with the need to select and use the driver appropriate for the particular printer available.
dropout
A missing piece of an image, or more generally, of a data stream. Dropouts can be caused by the improper use or function of a hardware device, by signal interference or disruption, or by other problems. A dropout in text transmission causes missing letters or words. A dropout in scanning can cause gaps in the image of a line. Scanning a fine line at too low a resolution or with too low a binary threshold is likely to cause dropouts in the resulting raster image of the line.
DTM
Digital Terrain Model. Elevation data in a 3 x 3 arcsecond grid form or a similar rectilinear form created by the Defense Mapping Agency.
DXF
Data Exchange format & format for storing vector data in ASCII or binary files. Used by Atuo CAD and other CAD software for dataenterchange. DXF files are convertible into ARC/INFO coverage.