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Glossary

The following is a list of some of the terms you may encounter when using Phoenix Maps Online. For a more thorough background on the world of Geographic Information Systems visit www.gis.com.


A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z

A
(top) address A physical location that can be used as the unique identification for a location.
 
  aerial photography A photograph, usually taken from an airplane, to record ground level events. Not to be confused with satellite remote sensing which produces digital images, aerial photography provides black and white, color and infrared photographs on film.
 
  arc An term that is used synonymously with line.
 
B
(top) basemap The basic features and layers that will be included on every map request made or printed.
 
  buffer The specific distance around the location you are focused on.
 
C
(top) CAD Computer-aided design. A computer-based system for the design, drafting, and display of graphical information. Also known as computer-aided drafting, such systems are most commonly used to support engineering, planning and illustrating activities.
 
  cartography The art and science of expressing graphically, usually through maps, the natural and social features of the earth.
 
  census block The smallest geographic entity for which the U.S. Bureau of the Census tabulates decennial census data. Visible and/or invisible features shown on a map prepared by the U.S. Census Bureau bound its geographic area. Many blocks correspond to city blocks bounded by streets, but blocks in rural areas may include many square miles and have some boundaries that are not streets. The Census Bureau established blocks covering the entire nation for the first time in 1990. Previous censuses back to 1940 had blocks established only for part of the nation.
 
  census geography The collection of various types of geographic areas used by the U.S. Bureau of the Census in its data collection and tabulation operations, including their structure, designations and relationships to one another. The largest unit of area is the entire United States, while the smallest is a census block.
 
  census tract A small, relatively permanent statistical subdivision of a county. Tract boundaries normally follow visible features, but may follow governmental unit boundaries or other non-visible features. Designed to be relatively homogeneous units with respect to population characteristics, economic status and living conditions at the time of establishment, census tracts average about 4,000 inhabitants.
 
  centerline A line digitized along the center of a linear geographic feature, such as a street or a river, that at a large enough scale would be represented by a polygon.
 
  center map A map tool that recenters the current map based on a selected point.
 
  centroid The geometric center of a feature. Of a line, it is the midpoint; of a polygon, the center of area; of a three-dimensional figure, the center of volume.
 
  city view A view in which the entire city of Phoenix and outlying suburbs is displayed.
 
  compass rose A small compass drawn on a map or chart, subdivided clockwise from 0 to 360 degrees with 0 indicating true north. On older maps and charts it was a decorated diagram of cardinal directions, divided into sixteen or thirty-two points. Originally called rosa ventorum, or "rose of the winds," it is sometimes still referred to as a wind rose.
 
  coordinate Coordinates generally represent locations on the earth's surface relative to other locations utilizing an X (horizontal) and Y (vertical) axis.
 
D
(top) datum In the most general sense, any set of numeric or geometric constants from which other quantities, such as coordinate systems, can be defined. A datum defines a reference surface. There are many types of datums, but most fall into two categories: horizontal and vertical.
 
  diameter A straight line segment passing through the center of a figure. The diameter of a circle is twice the distance of the circle's radius.
 
  digital elevation model (DEM) The representation of continuous elevation values over a topographic surface by a regular array of z-values, referenced to a common datum. Typically used to represent terrain relief.
 
  dimension A measurement in one direction. Specifically, one of three coordinates determining a position in space, or four coordinates determining a position in space and time.
 
  dragging Relocating display elements on a computer screen with a pointing device, such as a mouse. This can be done by pressing and holding a button (on the mouse) while moving the pointer on the screen.
 
E
(top) edgematching A spatial adjustment process that aligns features along the edge of one layer to features of an adjoining layer. The layer with the least accurate features is adjusted, and the adjoining layer is used as the control.
 
F
(top) Federal Geographic Data Committee (FGDC) An organization established by the U.S. Federal Office of Management and Budget responsible for coordinating the development, use, sharing and dissemination of surveying, mapping and related spatial data. The committee is comprised of representatives from federal and state government agencies, academia and the private sector. The FGDC defines spatial data metadata standards for the United States in its Content Standard for Digital Geospatial Metadata and manages the development of the National Spatial Data Infrastructure (NSDI).
 
  feature A set of points, lines or polygons in a spatial database that represent a real-world 'thing'. The terms feature and object are often used synonymously.
 
G
(top) geocoding The process of finding the location of a street address on a map. The location can be an x,y coordinate or a feature such as a street segment, postal delivery location or building. In GIS, geocoding requires a reference dataset that contains address attributes for the geographic features in the area of interest.
 
  GIS A computer system for capturing, storing, checking, integrating, manipulating, analyz 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.
 
H
(top)
I
(top) identify A map tool that allows you to click on a feature of the map and access any information about that feature that is contained in our databases.
 
J
(top)
K
(top)
L
 
  land information system (LIS) A commonly used term refering to a system for capturing, storing, checking, integrating, manipulating, analysing and displaying data about land and its use, ownership and development.
 
  latitude The angular distance, usually measured in degrees, along a meridian north or south of the equator. Lines of latitude are also referred to as parallels.
 
  layer Different types of geographic data are called "layers." Any number of layers may be viewed at one time, depending on the zoom level in the current map view. The order in which layers are displayed on a map is critical to visual presentation. For instance, if two polygon shapes overlap each other special care must be taken to make them both visible. This can be accomplished by making the uppermost layer "transparent" so that the color of the underlying layer can also be seen. Another method is to display the uppermost layer with "hash" lines, or a pattern of some kind so it is easily distinguished.
 
  legend The reference area on a map that lists and explains the colours, symbols, line patterns, shadings, and annotation used on the map. The legend often includes the scale, origin, orientation, and other map information.
 
  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 lines is synonymous with an arc.
 
  longitude The angular distance, expressed in degrees, minutes and seconds, of a point on the earth's surface east or west of an arbitrarily defined meridian (usually the Greenwich prime meridian). All lines of longitude are great circles that intersect the equator and pass through the north and south poles.
 
M
(top) map A graphic representation of features of the earth's surface or other geographically distributed phenomena. Examples are topographic maps, road maps, weather maps.
 
  map category (or map theme) A grouping of map features based on a specific topic. The following lists are a representative sample and do not reflect a complete list of the features for each category.

Recreation and Points of Interest:  Includes city-owned or public parks, mountain preserves, desert parks, sports complexes, swimming pools, golf courses, bikeways, light rail corridor, libraries and points of pride.

School Information:  Includes district, charter and private school information such as individual school locations, and district and attendance boundaries.

Neighborhoods:  Includes congressional and state legislative districts, parks, mountain preserves, desert parks, historic districts, Fight Back areas, neighborhood associations, redevelopment areas, family services and senior centers, libraries, fire and police stations.

Planning and Zoning:  Includes information about the physical development of the city such as the general plan, annexations, light rail corridor, zoning overlays, regulatory plan areas and zoning.

Transportation:  Includes streets, freeways, bikeways and bike bridges as well as the location of speed humps and the type of traffic signals on many intersections.

General Statewide Information:  Includes counties, incorporated and unincorporated cities and county seats. Most of the statewide information has been provided to the city by the Administration and Resource Analysis Division of the Administration and Resource Analysis Division of the Arizona State Land Department.

Return to home page.
 
  map unit The ground units of measurement-for example, feet, miles, meters or kilometers - in which the coordinates of spatial data are stored.
 
  meridian A great circle on the earth that passes through the poles, often used synonymously with longitude. Meridians run north-south between the poles. From a prime meridian or 0 degrees longitude (usually the Greenwich prime meridian), measures of longitude are negative to the west and positive to the east, where they meet halfway around the globe at the line of 180 degrees longitude.
 
N
(top) NAD83 North American Datum of 1983. A geocentric datum and graphic coordinate system based on the Geodetic Reference System 1980 ellipsoid (GRS80). Mainly used in North America, its measurements are obtained from both terrestrial and satellite data. Replaces the NAD27 coordinate system.
 
O
(top) orthophotograph A perspective aerial photograph from which distortions owing to camera tilt and ground relief have been removed. An orthophotograph has the same scale throughout and can be used as a map.
 
P
(top) pan A map tool that allows you to click and drag the map in any direction. To pan the map, move the cursor over the map, hold down the mouse button, and drag the map in any direction. Release the mouse button to leave the map in your desired position. The application will update the map display to fill in any blank areas revealed by your pan.
 
  parcel A tract or plot of land. The term is usually used in the context of land use or legal ownership.
 
  PDF Portable Document Format. A proprietary file format from Adobe which creates lightweight text-based, formatted files for distribution to a variety of operating systems.
 
  pixel The smallest element of a display device, such as a video monitor, that can be independently assigned attributes, such as color and intensity. The term is an abbreviation for picture element. Also, the smallest unit of information in an image or raster map. Usually square or rectangular, pixel is often used synonymously with cell.
 
  planar coordinate system A two-dimensional measurement system that locates features on a map based on their distance from an origin (0,0) along two axes, a horizontal x-axis representing east-west and a vertical y-axis representing north-south.
 
  plat A survey diagram, drawn to scale, of the legal boundaries and divisions of a tract of land.
 
  point 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 map.
 
  polygon A closed, two-dimensional figure with at least three sides that represents an area. It is used in GIS to describe spatial elements with a discrete area, such as parcels, political districts, areas of homogeneous land use and soil types.
 
  prime meridian In a coordinate system, any line of longitude designated as 0 degrees east and west, to which all other meridians are referenced.
 
Q
(top) query A statement expressing a set of conditions that forms the basis for the retrieval of information from a database.
 
R
(top) radius The distance from the center to the outer edge of a circle or circular curve.
 
  rubberbanding The process of click-n-dragging the cursor to form a box and then the elements of that area are displayed or used in an application.
 
S
(top) scale The relationship between distances on a map and the corresponding distances on the earth's surface expressed as a fraction or a ratio. One unit of measurement on the map -- 1 inch or 1 centimeter -- could represent 10,000 of the same units on the ground. This would be a 1:10,000 scaled map.
 
  spatial data Any information about the location and shape of, and relationships among, geographic features.
 
  State Plane Coordinate System A projected coordinate system used in the United States that divides each state into one or more zones to minimize distortion caused by the map projection. Also known as SPCS and SPC.
 
  symbol A graphic pattern used to represent a geographic feature on a map. For example, line symbols represent linear features; various marker symbols can represent points; shade symbols can represent areas; and text symbols, annotations. Many characteristics define symbols, including color, size, shape, angle and pattern.
 
T
(top) theme A user-defined perspective for geographic data.
 
  tract A small, relatively permanent statistical subdivision of a county. Tract boundaries normally follow visible features, but may follow governmental unit boundaries or other non-visible features. Designed to be relatively homogeneous units with respect to population characteristics, economic status and living conditions at the time of establishment, census tracts average approximately 4,000 inhabitants.
 
U
(top) United States Geological Survey - USGS National mapping agency of the United States. Produces paper maps, digital maps and DEMs for the entire nation at a variety of scales, including 1:24,000, 1:100,000, 1:250,000 and 1:1 million.
 
V
(top) vertex One of a set of ordered X,Y coordinates that defines a line or polygon feature.
 
W
(top) World Wide Web Consortium (W3C)
An organization that develops standards for the World Wide Web and promotes interoperability between Web technologies, such as browsers. Members from around the world contribute to standards for XML, XSL, HTML and many other Web-based protocols.
 
X
(top) x,y coordinates A pair of values that represents the distance from an origin (0,0) along two axes, a horizontal axis (x) representing east-west, and a vertical axis (y) representing north-south. On a map, x,y coordinates are used to represent features at the location they are found on the earth's spherical surface.
 
  x-axis In a planar coordinate system, the horizontal line that runs right and left (east and west of) the origin (0,0). On a chart, the horizontal axis.
 
Y
(top) y-axis In a planar coordinate system, the vertical line that runs above and below (north and south of) the origin (0,0). Numbers north of the origin are positive, and numbers south of it are negative.
 
Z
(top) zoom in A map tool that allows you to zoom in (and re-center the map) on the position on the map where you click, or to an area you define by dragging a box in the map. The Zoom-In tool is turned on by default when you start the application.
 
  zoom out This tool allows you to zoom out (and re-center the map) from the position on the map where you click, or from an area you define by dragging a box in the map.
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