P

palette

Total range of colours which may be displayed -- not necessarily all at once. 

partitioning

Division of a coverage into smaller regular parts. If this coverage is represented by a vector structure then the topology should be reconstructed appropriately. 

pattern

Predefined or user specified graphic design displayed along a linear feature or used to fill an area. 

PDES

Product Data Exchange Specification (is the result of activity by the US National Bureau of Standards and the International Standards Organization (ISO). 

pel

Same as pixel. See pixel. 

pen plotter

See plotter. 

perimeter measurement

See measurement -- perimeter. 

peripheral

Any physical device connected to a computer. 

photogrammetry

Science of data and measurements from photographs and sensing systems. 

photomap

Aerial photograph with cartographic data and enhancements added. 

pitch

Number of printed characters per inch. 

pixel

Refers to picture element. Is the most basic element in an image or grid map. The words PIXEL and CELL are often used interchangeably in the GIS field. 

planimetric data

Data which does not take into account elevation for determining position (2-D data). 

planimetric map

Map showing only planimetric data. 

plat

Diagram (drawn to scale) showing relevant data, boundaries, and subdivisions of a tract of land. Information is obtained from survey. 

plotter

Display device which draws images on paper. Usually uses ink pens but may also use technology similar to that in photocopy machines. 

point -- geographic

Geometric element identifying a spot (location). In a GIS, a point may be defined in a variety of manners (actual point structure, degenerate line, or degenerate polygon). 

point pattern

Refers to the spatial arrangement of points. 

point-and-click interface

Refers to graphical user interface which uses pull-down (or similar) menu or icons, and a mouse. 

polygon

Closed figure representing an area on a map. A polygon can be represented by a single arc or string which closes upon itself. 

polygon generation

Process of connecting together linear features to produce polygon (area) features. Is a component of topology generation. See Topology, Topology Generation. 

polyline -- graphics

Single entity which is made up of a number of connected lines. 

postal code -- Canada

Addresses in Canada have an associated postal code for mailing purposes. It is composed of six alphanumeric characters taking the form "ANA NAN", where "A" is a letter of the alphabet (from A to Z) and "N" is a numeric (0 to 9). Common practice is to use a space to separate the first three characters from the last three. The first three characters are known as the Forward Sortation Area (FSA) and the last three characters are known as the local delivery unit (LDU). In a large municipal area, the FSA describes an area roughly the size of 25 letter carrier routes; the LDU specifies a block face, a portion of a block face, or a location within a block face (such as an apartment building, a business or other organization, or postal service). Postal codes may be used for nominal geocoding. 

precision -- computer data

Number of significant digits of information. Data precision depends upon the number of data bytes used to store the information and the internal format of the data. 

processing mode

Refers to the way a user processes information on a system (either interactive or batch). 

profile analysis

Extraction and display (from DTM data) of a profile given a specified line and orientation. Same as cross-section. 

programmers interface

Set of function calls or routines which allow a program to access GIS data, files, and functions or commands. Programmers interface allows for the compilation of custom programs to meet specific application needs (also known as a High Level Language Interface). 

projections -- map

Projections involve the mapping of points between a sphere (representing the earth) and plane (flat) surfaces. Forward projections indicate transformation from sphere to plane. Reverse, indicate a mapping from plane to sphere. 

prompt

System message to the user indicating a response is required. 

protection facilities

General ability of the system to restrict operations performed by the user on data files or restrict user access to data files. Restricted File Access specifically refers to a systems ability to allow only certain operations to be performed on a data file. E.g., read only. Restricted User Scope specifically refers to a systems ability to restrict access to certain users and within that set of users to certain data files and system operations. 

proximal polygons

Splitting up of a study area such that all points in the area are grouped into tiles according to the minimum distance between them and a previously determined point. That is all points within the tile are closest to one given sampled point than any other sampled point. The process is based on Delaunay triangulation to which it is "dual" in nature. Proximal Polygons are also known as Voronoi Polygons, Thiessen polygons, or Dirichlet tessellation. 

proximity analysis -- vector

As a vector operation -- operation which identifies features within a specified distance from given other features or are closest to a given feature. 

puck

Small hand-held device (often with several function buttons) used for entering data from a digitizing table. May also be referred to as a "cursor". This should not be confused with the screen (CRT) cursor. 

pull-down menus

Interface which uses key words (usually at the top of the screen) to identify menus which the user can make appear below (the key word). 

pull-over menus

Similar to pull-down menus except key words appear as a column at the left or right of the screen and new menus appear right or left of the key word selected. 

Q

quadtree

Term used to describe a class of hierarchical data structures based on the principle of recursively decomposing an image into mutually exclusive quarters or quads until a region is homogeneous or until some specified level has been reached. 

R

raised contours

See relief map. 

raster

Refers to a coverage partitioned into a set of grid cells (usually square) with each cell assigned a value describing some spatially related characteristic (e.g., land use). Usually when the word "raster" is used, the cells are organized by rows. 

raster -- global operators

Functions which are performed on the whole geographic extent of the coverage or which require spatial information based on the extent of the coverage. 

raster -- local operators

Operators which are neighbourhood in scope (operate on a limited subset of the image). This usually involves the calculation and assignment of a value to a cell as a function of the surrounding cell values. Common operations involve moving average, smoothing, and edge enhancement. 

raster -- unary operator

Operator which acts on a single cell or element of a grid. Classification is an example of an unary operator. 

raster to vector conversion

Conversion of raster encoded point, line and/or polygon features to vector format. The word "vectorize" is also used to describe this process. 

rasterization of vectors

See vector-to-raster conversion. 

rdbms

Acronym for Relational DataBase Management System. A database management system which operates on relational structured data. See database management system. 

records management

In general, the creation, the maintenance, and the destruction of an organizations records (traditionally on paper). 

rectification

Process of removing the effects of tilt, relief, and other distortions from map data (or images). 

reflection test -- data exchange

Test in which system data is converted to a neutral format and then converted from the neutral format back into the system format. The initial data and the subsequent "converted" data should be identical (symmetry). 

region

Area of the earth's surface possessing some characteristic. 

relational database structure

Refers to the arranging of information into sets so that relations between different sets can be used to provide access and transformation. 

relief

Standard deviation derived from elevations. It gives information on the variability of elevation. 

relief map

Map that appears to be three dimensional and shows the elevations and depressions of a surface. 

remote sensing

Techniques for recording and evaluating the earth's surface via sensed aerial or satellite data. 

resolution

Smallest spacing between two displayed points or the smallest size which may be sampled and distinguished or measured. 

RLE

See run length encoding. 

rotation

Geometric transformation involving a change of orientation. 

rubbersheeting -- local/global

Rectification of graphic file coordinates to make them conformable with selected control points. This operation may be performed globally on the entire coverage or locally on a small portion of the data set. 

run length encoding (RLE)

Data structure often used for storing information in a raster database. Data is stored in a compressed form (consisting of a value and the number of times it should be repeated - its run) thus reducing storage requirements. A variation on this theme is to store a value, start location, and end location. 

S

SA-STF

South African - Spatial Transfer Format. The South African standard is based on a relational model (i.e., relational tables are exchanged). 

scale

Ratio or relationship of the distance on a map, chart, or photograph to the corresponding distance on the ground -- the real world. 

scaling

A geometric transformation. Involves multiplying the coordinates by numeric factors. 

SDTS

See US-SDTS. 

seamless data

GIS data storage which is independent of map sheets -- seamless. 

section -- municipal

Unit of subdivision of a municipality. Usually one mile square. 

seed point

Point identifying an area (polygon). Often the terms SEED POINT and CENTROID are used interchangeably in the GIS field. The location of seed points may be calculated automatically or may be assigned manually by the user. 

selection -- by attribute

Selection of coverage features by specifying an attribute value or range. 

selection -- by cursor

Selection of a coverage feature by pointing to it with a cursor. 

selection -- by display characteristics

Selection of coverage features by specifying graphic display characteristics. 

selection -- by location

Selection of a coverage feature by specifying its geographic location. 

selection -- by window

Selection of coverage features by specifying a geographic window. 

SET

Standard d'Echange et de Transfert - Data Exchange and Transfer Standard (a development effort by Aerospatiale and the European aerospace industry. 

shell

Overlying program from which all other system modules and functions can be accessed. 

site analysis

Set of techniques (programs and procedures) used to determine the characteristics or suitability of a site or location for a particular purpose. 

slivers

Refers to tiny polygons which are formed when the sides of two adjacent polygons do not totally match up. Often Slivers are considered spurious in nature. 

slope

Gradient of elevation. One of the characteristics of terrain elevation. See gradient. 

smoothing

Techniques/procedures for removing small erratic changes from data. This is usually applied to line and surface data. In mapping applications this is often used to create a better visual product -- may be referred to as smoothed data. 

snapping -- function

See line snapping. 

soft error recovery

Indicates that the system does not halt or crash upon an error occurring but rather returns to the command level; displays a meaningful message; allows the user to identify the source of the error; and allows the user to rectify the condition. 

software conformance

Conformance deals with ensuring that software is implemented and tested such that it meets specifications. Usually involves falsification testing, using sample cases that test as many of the specifications as feasible. The suite of test data (validation suite) tries to find errors in the implementation. If errors are found then the implementation does not conform to the specification. The absence of errors does not necessarily mean the converse. Absence of errors may mean the test suite was not extensive enough to find all errors. Falsification testing can determine non-conformance to a standard but not assure total and complete conformance. 

solid modeling

Techniques used to create, represent, and display 3-D shapes using a computer. Primarily used for design purposes. 

spaghetti data

Data which is organized without coherent structure. 

spaghetti digitizing

Refers to the digitizing of map features (points and lines) without any regard to sequence or identification of line intersections. 

SPARC

Scalable Performance ARChitecture. A high performance reduced instruction set computer from Sun Microsystems. A number of GIS products now operate on SPARC workstations. 

Spatial Data Transfer Standard (SDTS)

See US-SDTS. 

spatial entity

A real world "thing" which cannot be subdivided into "things" of the same kind. Examples: bridge, house, lot. 

spatial statistics

Branch of applied statistics dealing with the quantification and modelling of spatial phenomena. 

splitting

See Partitioning. 

SQL

Structured Query Language. Language/commands used to interact with a relational database. 

STEP

Standard for The Exchange of Product data (an international standard which is currently being discussed and which will be an outgrowth of VDA-FS (a German standard being developed by the automotive industry), SET, and PDES. 

stereo plot

Involves the generation of two images with a difference of view or separation of 2 to 5 degrees. The images are viewed by means of a stereo viewer. 

street network -- model

Street structure or street network can be modeled in a number of different ways depending upon use (or the kinds of functions which are important). It may be modeled in an "atomic" manner (block faces, corners, ...) or at a larger network scale (R.O.W.'s, intersections, ...). 

sun shading

DTM display technique where slopes are shaded as if they were illuminated by a light source. 

surface modeling

Process of generating or interpolating a surface given a set of x,y,z points. 

system architecture

Overall configuration and design of a system from data structures to operating procedures. 

system command access

Ability to evoke operating system commands and procedures while within a sub-system. 

T

terrabyte

One thousand gigabytes. 

tessellation

Process of splitting an area into tiles. 

thematic map

Map showing information on only one topic. E.g., temperature, rainfall, population, etc. 

thiessen polygons

See proximal polygons. 

thinning

See weeding. 

TIGER

Topologically Integrated Geographic Encoding and Referencing. System and database developed by the U.S. Department of Commerce. Is meant to be used as a digital map base to support the activities of the Census Bureau. Will replace GBF/DIME. 

tiles

Refers to small planar polygons used to cover a surface. An element of tessellation. 

TIN

See digital terrain model - TIN 

Shape or configuration of the land surface or sea bottom. 

topological errors

Errors in the spatial data structures which do not allow for acceptably defined topology. 

topological map

Map where distance and direction are subject to change and variation. Relationship between points is maintained. Famous example of a topological map is the London (United Kingdom) underground transit system. 

topology

Way in which geographic elements are structured or connected together; a mathematical representation of spatial relationships among geographic entities. 

topology generation

Process of generating topological relationships between elements of a coverage. 

toponomy

Term is used to refer to the place-names of a region, country, or district (properly "as a subject of study"). 

transformation

In general, in GIS, the mathematical converting of position from one coordinate system to another. 

translation

Geometric transformation involving a linear shift in location. 

transmission test -- data exchange

Test in which data in one system is converted to a neutral format and transmitted to a second and different system. A concern here is how to quantify or measure the similarity or difference of the data on the two different systems. 

triangulated irregular network (TIN)

See digital terrain model -- TIN. 

U

UK-NTF

United Kingdom - National Transfer Format. This format allows for vector data to be transferred either unstructured or structured with few or many attributes. The format allows for extensive header information and quality information. 

updating -- gis

Process of changing the graphic characteristics or attributes of a feature. 

updating -- operational system mode

May be performed interactively under the control of a user or as a batch process where changes are made on a selected set of data elements. 

upload

Process of transmitting data from a micro-computer or workstation to a larger central computer or file server system. 

URISA

Urban and Regional Information Systems Association. Professional society composed primarily of administrators and technical individuals from municipal and regional governments. Sponsor a number of workshops and conferences with heavy emphasis on GIS related issues. 

US-SDTS

United States - Spatial Data Transfer Specification. US-SDTS covers both vector and raster data. It supports 0, 1, and 2 dimensional elements (points, lines, and areas). A very large range of spatial entities or objects are allowed for. Vector data may be structured in either a relational or hierarchical manner for exchange. 

user interface

The manner in which the system communicates and interacts with the user -- the way information is presented to the user and way replies are solicited from the user. 

USGS

United States Geological Survey. U.S. agency which collects and supplies a large amount of digital geographic related data. 

V

VDT

Video Display Terminal. See video display terminal. 

VDU

Video Display Unit. See video display terminal. 

vector

Quantity having both magnitude and direction. In most GIS cases it is represented as an ordered pair of points. 

vector data structure

Use of x,y coordinates to describe points, lines, and polygons. The information describing the connections and relationships (topology) between the points, lines, and polygons may be explicitly determined and stored with the coordinates depending on the system and its uses. 

vector to raster conversion

Conversion of points, lines and/or polygons from vector format to raster format. This is commonly known as rasterization. 

video display terminal (VDT)

Terminal with display screen and keyboard. 

voronoi polygons

See proximal polygons. 

W

WAN

See wide area network. 

weeding

Process to reduce the number of points used to represent a line. Purpose of this process is to reduce storage space requirements and/or reduce later computation time (less points can mean less computation). 

wide area network

Network which interconnects over large geographical regions -- often over telephone lines. 

WIMP interface

Graphical user interface which uses: W -- windows; I -- icons; M -- mouse; P -- pull-down type menus. 

windowing

Use of a (usually) rectangular area to select part of a coverage for display, transformation, or analysis. The area selected may be compiled into a new coverage. 

workstation

High performance micro-computer. Usually single user and dedicated to a specific application. The line between high-end personal micro-computers and low-end workstations is vague. 

X Y Z

zoom

Ability to enlarge or reduce the image of a map (or other figure) presented on a CRT display. Often the terms "zoom in" and "zoom out" are used to mean "make larger" and "make smaller". 

#

0-cell

Point of intersection, termination, or change in a set of one or more 1-cells. Term has been used in description of U.S. data exchange standards specifications. 

1-cell

A line defined by two 0-cells. The line may or may not be straight (it may be defined by a set of points). Term has been used in description of U.S. data exchange standards specifications. 

2-cell

A polygon enclosed by a sequence of 1-cells. A 2-cell may contain 1-cells which are directly or indirectly connected to one of the bounding 1-cells. A 2-cell may contain one or more unconnected 2-cells (these are commonly referred to as islands). Term has been used in description of U.S. data exchange standards specifications. 

3270

Often used to refer to the communications protocol used to connect interactive terminals to IBM mainframes. 

4GL

See fourth generation language. 

 

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