*** Address: A means of referencing an object for the purposes of unique identification and location.
* ASCII: (American Standard Code for Information Interchange) -- This is the de facto world-wide standard for the code numbers used by computers to represent all the upper and lower-case Latin letters, numbers, punctuation, etc. There are 128 standard ASCII codes, each of which can be represented by a 7 digit binary number: 0000000 through 1111111.
*** Attribute: A trait, quality or property describing a geographical feature. A fact describing an entity in a relational data model, equivalent to the column in a relational table.
*** Attribute table: A tabular file containing rows and columns. Attribute tables are normally associated with a class of geographic features. Each row represents a geographic feature. Each column represents one attribute of a feature, with the same column representing the same attribute in each row.
*** Automation: Any process whereby hardcopy cadastral, planimetric, or topographic features are converted into a digital format for use within a GIS.
*** Automated Digitizing: Conversion of a map to digital form using a method which involves little or no operator intervention during the digitizing stage, for example scanning for raster images or automatic line following for vector images.
*** Base map: A set of topographic data displayed in map form providing a frame of reference or contextual information to the user.
CAD: see Computer Aided Design.
CAMA: see Computer Assisted Mass Appraisal.
*** Cadastral map: A map showing the boundaries of the subdivisions of land for purposes of describing and recording ownership and taxation.
*** Centroid: The geometric centre of a polygon. Calculating the centre of an irregularly shaped polygon requires the use of geometrical algorithms. In spatial information systems, the centroid is a point in a polygon to which attribute information about that specific area is linked.
*** Check plot: A graphic output used to verify either the content or positional accuracy of digital data by direct superimposition on the graphic original used to create the digital record.
*** COGO: A set of procedures for encoding and manipulating bearings, distances and angles of survey data into co-ordinate data. COGO is frequently a subsystem of GIS.
*** Computer Aided Design: The design activities, including drafting and illustrating, in which information processing systems are used to carry out functions such as designing or improving a part or a product.
Computer Assisted Mass Appraisal: an automated system for maintaining property data, valuing property, notifying owners, and ensuring tax equity through uniform valuations.
*** Coordinate System: A recognized reference system for the unique location of a point in space. A co-ordinate system is usually defined by a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian, and possible shifts in the X and Y directions to locate X,Y positions of point, line, and area features.
*** Coverage: A term that refers to a set of spatial data within a Geographical Information System. Also known as a layer or spatial dataset.
** Database: A collection of information organized in such a way that a computer program can quickly select desired pieces of data; an electronic filing system.
*** Database management system: A collection of software for organizing the information in a database. Typically a DBMS contains routines for data input, verification, storage, retrieval and combination.
*** Data capture: The encoding of data. In the context of digital mapping this includes digitizing, direct recording by electronic survey instruments, and the encoding of text and attributes.
*** Data format: A specification that defines the order in which data is stored or a description of the way data is held in a file or record.
*** Datum: 1) Any point, line, or surface used as a reference for a measurement of another quantity. 2) A model of the earth used for Geodetic calculations.
DDE: see dynamic data exchange
*** Digital Data: Data representing distinct objects or digits that stand for some phenomenon in the real world. Data represented digitally may be manipulated to produce a calculation, sort, computation, or query.
*** Digitizer: A device for manual digitizing. It normally consists of a flat surface that documents can be attached to, and a cursor or puck that is used to locate and input map features into the computer.
*** Digitizing: A method of data capture that involves the conversion of data in analog form, such as maps and aerial photographs, into a digital form that is directly readable by a computer. This is normally achieved manually by a human operator using a digitizer, although methods of automated digitizing and semi-automated digitizing also exist. The result of digitizing is a digital map in vector form.
** Dynamic Data Exchange: a form of interprocess communication where two or more programs can exchange information and commands.
*** Emulator: a software package or program which imitates the functions of a hardware device or other software, normally another computer. For example, a terminal emulator allows a user to execute programs designed for one type of terminal from another type of terminal. Terminal emulators are commonly used to interface PC's with mini- and mainframe computers.** Enterprise: literally, a business organization. In the computer industry, the term is often used to describe any large organization that utilizes computers. An intranet, for example, is a good example of an enterprise computing system.
* Ethernet: A very common method of networking computers in a LAN. Ethernet will handle about 10,000,000 bits-per-second and can be used with almost any kind of computer.
FAT: see feature attribute table
*** Feature: A set of points, lines or polygons in a spatial database that represent a real-world entity. The terms feature and object are often used synonymously.
Feature Attribute Table: Attribute data organized into a field and record structure.
*** Field: A set of one or more alphanumeric characters comprising a unit of information.
A specific class of information within a database, for example, in a database of employees, one field may be 'employee_surname', another might be 'date_of_birth'. Synonymous with column.** Flat file: A relatively simple database system in which each database is contained in a single table.
*** Foreign key: One or more attributes that can uniquely identify a record in another table within a database. A foreign key is the primary key of another table. Foreign key-primary key relationships define a relational join.
*** Geographic Information System: A computer system for capturing, storing, checking, integrating, manipulating, analyzing and displaying data related to positions on the Earth's surface. Typically, a Geographical Information System (or Spatial Information System) is used for handling maps of one kind or another. These might be represented as several different layers where each layer holds data about a particular kind of feature. Each feature is linked to a position on the graphical image of a map. Layers of data are organized to be studied and to perform statistical analysis. Uses are primarily government related, town planning, local authority and public utility management, environmental, resource management, engineering, business, marketing, and distribution.
*** Georeference: To establish the relationship between page co-ordinates on a planar map and known real-world co-ordinates.
*** GIS: see Geographic Information System.
*** Global Positioning System: A satellite based navigational system allowing the determination of any point on the earth's surface with a high degree of accuracy given a suitable GPS receiver. The network of satellites is owned by the US Department of Defense, and as such, the accuracy of the signal is intentionally degraded for non-US military users. The error introduced into the signal is known as selective availability. Error in the accuracy of GPS derived positions can also be introduced through the nature of local conditions.
GPS: see Global Positioning System.
*** Hardware: All or part of the physical components of an information processing system. For example, hardware might include the monitor, printer/plotter, network, digitizing tables, scanners as well as the computers themselves.
*** Integration: the combining of data of different types from different sources and systems to provide new information.
*** Layer: A usable subdivision of a dataset, generally containing objects of certain classes, for example rivers, roads or geology.
*** Line: A set of ordered coordinates that represent the shape of geographic features too narrow to be displayed as an area at the given scale (contours, street centerlines, or streams), or linear features with no area (county boundary lines). A line is synonymous with an arc.
** Macros: simple programs or batch files; a symbol, name, or key that represents a list of commands, actions, or keystrokes. Many programs allow you to create macros so that you can enter a single character or word to perform a whole series of actions.
NAD: see North American Datum.
*** Network: Any time you connect 2 or more computers together so that they can share resources, you have a computer network. Connect 2 or more networks together and you have an internet; (1) An interconnected set of arcs or lines representing possible paths for the movement of resources from one location to another; (2) A group of computers that are linked, and are able to share peripherals, software and data. The Internet is probably the most well known example of a computer network; (3) A type of database structure. A network data model is based upon the idea of explicit links between related entities.
*** North American Datum: The official reference ellipsoid used for the primary geodetic network in North America.
** Object Linking and Embedding: a compound document standard developed by Microsoft Corporation. It enables you to create objects with one application and then link or embed them in a second application. Embedded objects retain their original format and links to the application that created them.
ODBC: see Open Database Connectivity
OLE: see Object Linking and Embedding
*** One-to-many relationship: A relate in which one record in a table is related to many records in another table. This is the most common form of relate, as one-to-one and many-to-many relates are undesirable within an RDBMS.
** Open Database Connectivity: a standard database access method developed by Microsoft Corporation. The goal of ODBC is to make it possible to access any data from any application, regardless of which database management system (DBMS) is handling the data.
*** Open system: An information processing system that complies with the requirements of open systems interconnection (OSI) standards in communication with other such systems.
** Operating system: the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.
*** Orthophotograph: A modified copy of a perspective photograph of the earth's surface with distortions due to tilt and relief removed.
*** Oracle: A relational database management system.
*** Overlay: The process of superimposing two or more maps, through registration to a common co-ordinate system, such that the resultant maps contain the data from both maps for selected features. Although the term overlay can be applied to paper based maps, more often it applies to the use of digital data, nevertheless, the principal is the same.
*** Overshoot: A topological error where a line projects beyond the true intersection with another line.
*** Parcel: An area of land, usually with some implication for land ownership or land use.
PLSS: Public Land Survey System
*** Pixel: 1) A contraction of the words picture element. Pixel refers to the smallest unit of information available in an image or raster map. 2) The smallest element of a display device that can be independently assigned attributes such as color and intensity.
*** Point: A zero-dimensional abstraction of an object represented by a single X,Y coordinate. A point normally represents a geographic feature too small to be displayed as a line or area; for example, the location of a building location on a small-scale map, or the location of a service cover on a medium scale map.
*** Polygon: A feature used to represent areas. A polygon is defined by the lines that make up its boundary and a point inside its boundary for identification. Polygons have attributes that describe the geographic feature they represent.
*** Primary key: One or more attributes whose values uniquely identify a row in a database table. Also the constraint used to enforce that these column(s) are not nullable and are unique.
** Proprietary data formats: privately owned and controlled. In the computer industry, proprietary is the opposite of open. A proprietary design or technique is one that is owned by a company. It also implies that the company has not divulged specifications that would allow other companies to duplicate the product.
*** Puck: A hand-held device on a digitizing table or tablet used for picking menus or accurately digitizing graphic objects.
*** Query: A statement expressing a set of conditions that forms the basis for the retrieval of information from a database. Queries are often written in a standardized language such as SQL.
RDBMS: see relational database management system
*** Relate: The relating of two or more tables in a relational database on the basis of a common item or field. Rows from these tables are compared, and based upon certain specified criteria, rows may be retrieved, updated or deleted from the database. One of the most common forms of join operation is the equijoin, where the values in one table must match the values in another. SQL is a common language employed for performing join operations using relational databases.
*** Raster Data: An abstraction of the real world where spatial data is expressed as a matrix of cells or pixels, with spatial position implicit in the ordering of the pixels. With the raster data model, spatial data is not continuous but divided into discrete units. This makes raster data particularly suitable for certain types of spatial operation, for example overlays or area calculations. Unlike vector data however, there are no implicit topological relationships.
Relational database: a database that allows descriptive information to be entered in the same database as geographic information.
*** Relational database management system: A database management system with the ability to access data organized in tabular files that can be related to each other by a common field. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.
*** Scanning: A method of data capture whereby an image or map is converted into digital raster form by systematic line-by-line sampling using a scanner.
** Scripting language: a simple programming language with which you can write scripts.
*** Seamless database: A digital database storing, as one continuous data structure, spatial information spanning two or more disjointed map sheets.
*** Software: programs, procedures and rules for the execution of specific tasks on a computer system.
Spatial data: Any information about the location and shape of, and relationships among, geographic features. This includes remotely sensed data, map data, and digital data. In the context of digital data, the term may refer to a coverage, theme, or layer.
SQL: see Structured Query Language
* Structured Query Language: A specialized programming language for sending queries to databases. Most industrial-strength and many smaller database applications can be addressed using SQL. Each specific application will have its own version of SQL implementing features unique to that application, but all SQL-capable databases support a common subset of SQL.
*** Spatial Data: Also known as spatial dataset, coverage, and layer. Data pertaining to the location of geographical entities together with their spatial dimensions.
**** State Plane Coordinate System: The plane-rectangular coordinate systems established by the United States Coast and Geodetic Survey, one for each state in the US, for use in defining postions of geodetic stations in terms of planar x and y coordinates. Massachusetts State Plane Coordinate System is based upon the Lambert conformal conic map projection, NAD 1983.
* TCP/IP: (Transmission Control Protocol/Internet Protocol) this is the suite of protocols that defines the Internet. Originally designed for the UNIX operating system, TCP/IP software is now available for every major kind of computer operating system. To be truly on the Internet, your computer must have TCP/IP software.
*** Thematic map: A map depicting selected kinds of information relating to one or more specific themes. Examples are soil type, land classification, population density and rainfall maps.
*** Theme: A user-defined perspective on a geographic dataset specified, if applicable, by a name and feature class or dataset name, attributes of interest, or data classification scheme.
*** Topology: The relative location of geographic phenomena independent of their exact position. In digital data, topological relationships such as connectivity, adjacency and relative position are usually expressed as relationships between nodes, links and polygons. For example, the topology of a line includes its from- and to-nodes, and its left and right polygons. Topology is useful in GIS because many spatial modeling operations don't require coordinates, only topological information. For example, to find an optimal path between two points requires a list of the lines or arcs that connect to each other and the cost to traverse each line in each direction. Coordinates are only needed for drawing the path after it is calculated.
*** Undershoot: A line feature, which is short of its true intersection with another line feature.
Unique identifier: a data item or field common to at least two databases chosen to perform a relate, link or join.
* UNIX: A computer operating system (the basic software running on a computer, underneath things like word processors and spreadsheets). UNIX is designed to be used by many people at the same time (it is multi-user) and has TCP/IP built-in. It is the most common operating system for servers on the Internet.
*** Vector data: An abstraction of the real world where positional data is represented in the form of coordinates. In vector data, the basic units of spatial information are points, lines and polygons. Each of these units is composed simply as a series of one or more co-ordinate points, for example, a line is a collection of related points, and a polygon is a collection of related lines.
* (http://www.matisse.net/files/glossary.html) Matisse Enzer 1999 "Glossary of Internet Terms"
** (http://webopedia.internet.com/) PC Webopaedia "The #1 online encyclopedia and search engine dedicated to computer technology"
*** ( http://www.geo.ed.ac.uk/agidict/alpha.html) Association for Geographic Information "GIS Dictionary"
**** New York State Archives and Records Administration. "Local Government GIS Development Guides: Manager's Overview, Needs Assessment, Conceptual Design of the GIS." Albany, New York. 1996.