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 |
| Absolute Map Accuracy: The degree to which objects on a map are positioned at
their true ground locations relative to a coordinate system, such as geographic
coordinates (latitude and longitude) (see Relative Map Accuracy). |
| Aerial Photography: Photographs of a part of the earth's surface taken by a
camera mounted in an aircraft for mapping purposes. This usually consists of a series of
overlapping vertical photos taken in strips which can form the basis for mapping. |
| Attribute: Alphanumeric (non-graphic) data related to a specific map feature
(point, line or polygon). For example, parcel information linked to a specific parcel
(polygon) might include the parcel owner's name and the parcel address. |
| B |
| Base Data: Basic level of data or features on a base map. |
| Base Map: A term which varies in different applications, but, in general,
refers to a map that depicts the fundamental map elements, such as streets, buildings,
streams, etc., which are used frequently for locational reference. It is the control
document from which various other maps in a geographic information system are developed. |
| C |
| Cadastre: A system that defines the legal characteristics of properties, such
as ownership, title issues, value, etc. |
| Contour: A line connecting points of equal surface value. |
| Contour Interval: The difference in surface values between contours. |
| Coordinate: A set of numbers that designate location in a given reference
system, such as x,y in a planar coordinate system or an x,y,z in a three-dimensional
coordinate system. Coordinates represent locations on the Earth's surface relative to
other locations. |
| Coordinate Systems: A framework used to define the positions (locations) of
points in space either in two or three dimensions. |
| Coverages: One of a series of data themes, such as wetlands or water lines, in
a geographic information system with graphic and attribute data related to that topic. |
| D |
| Database: A logical collection of interrelated 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 location and shape of geographic features
recorded as points, lines, areas, or pixels, as well as their attributes. |
| Database Management System (DBMS): A systematic approach to creating,
maintaining, accessing, reporting, and analyzing attribute (alphanumeric or text) data. |
| Datum: In mapping, a numeric or geometric quantity which serves as a reference
or base to accurately define other quantities. It most often refers to either a horizontal
standard, such as a particular spheroid for referencing coordinate positions, or it refers
to a vertical datum, such as mean sea level, from which elevations are referenced. |
| Digital Elevation Model (DEM): A digital representation of a continuous
variable over a two-dimensional surface by a regular array of z values referenced to a
common datum. Digital elevation models are typically used to represent terrain relief. |
| Digital Map: A computer-readable representation of a geographic area or
phenomenon that can be displayed or analyzed by a digital computer. This is in contrast to
an analog "paper" map. |
| G |
| Geographic Feature: A user-defined geographic phenomenon that can be modeled or
represented using geographic data sets. Examples of geographic features include streets,
sewer lines, manhole covers, accidents, lot lines, and parcels. |
| Geographic Information System (GIS): An organized collection of computer
hardware, software, geographic data and personnel designed to efficiently capture, store,
update, manipulate, analyze and display all forms of geographically referenced
information. Certain complex spatial operations are possible with a GIS that would be very
difficult, time-consuming or impractical otherwise. |
| Geoid: The figure of the earth considered as a sea level surface extended
continuously through the continents. It is a theoretically continuous surface that is
perpendicular at every point to the direction of gravity (the plumb line) (see Datum). |
| Georeference: To establish the relationship between page coordinates on a
planar map and known real-world coordinates. |
| Global Positioning System (GPS): A constellation of satellites originally
developed by the U.S. Department of Defense as a navigation aid. It is now used by the
civilian community for navigation and horizontal/vertical positioning of features. |
| Graphic Database: A collection of digital descriptions of map features (points,
lines/arcs, areas/polygons, pixels/grid cells), symbols and annotations which can be used
to generate a display. This is in contrast to an attribute database (see Attribute). |
| H |
| Horizontal Datum: The two most common spheroidal reference surfaces in Canada
used as a reference or base to accurately define horizontal positions (x,y or longitude,
latitude) are the North American Datum of 1927 (NAD27) or the more recent and precise
North American Datum of 1983 (NAD83) (see Datum). |
| Hydrography: The representation of the location and direction of flow of water
bodies. In geographic information systems, it usually refers to coverages depicting
various water features. |
| I |
| Image: A graphic representation or description of a scene, typically produced
by an optical or electronic device. Common examples include remotely sensed data (e.g.,
satellite data), scanned data, and photographs. An image is stored as a raster data set of
binary or integer values that represent the intensity of reflected light, heat, or other
range of values on the electromagnetic spectrum. |
| L |
| Latitude: The angular distance of a location north or south of the equator. |
| Layers: A logical separation of mapped data usually representing a theme, such
as roads, political boundaries, etc. Layers are all registered to one another by means of
a common coordinate system. |
| Legend: The reference area on a map that lists and explains the colors,
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 represents the shape of geographic
features too narrow to be displayed as an area at the given scale (e.g., contours, street
centerlines, or streams), or linear features with no area (e.g., province and municipality
boundary lines). |
| Longitude: The angle between the plane of a meridian and the plane of an
initial meridian arbitrarily chosen (the Greenwich Prime Meridian). In Canada, this angle
is commonly measured as the angle west of the Prime Meridian. |
| M |
| Map: An abstract representation of the physical features of a portion of the
Earth's surface graphically displayed on a planar surface. Maps display signs, symbols,
and spatial relationships among the features. They typically emphasize, generalize, and
omit certain features from the display to meet design objectives (e.g., railroad features
might be included in a transportation map but omitted from a highway map). |
| Map Accuracy: A measure of the maximum errors permitted in horizontal positions
and elevations shown on maps. |
| Map Scale: The relationship existing between a distance on a map and the
corresponding distance on the earth. A scale of 1 inch = 2000 feet can also be expressed
as 1:24,000 (i.e., 1 inch on the map to 24,000 inches on the earth). |
| Map Units: The coordinate units in which a geographic data set is stored. Map
units can be inches, centimeters, feet, meters, or decimal degrees. |
| Meridian: A line on the earth's surface which follows the shortest distance
from pole to pole. |
| N |
| North American Datum (NAD): There are two North American Datums: North American
Datum of 1927 (NAD 27) and North American Datum of 1983 (NAD 83). Both are geodetic
reference systems, but each is based on different measurements. NAD 27 incorporated all
horizontal geodetic surveys completed up to 1927. NAD 83 updated NAD 27 with current
measurements using radio astronomy and satellite observations. NAD 83 positions are
consistent with satellite location systems (see GPS, Datum, Horizontal Datum). |
| O |
| Orthophotography: An aerial photograph in which the distortions due to camera
tilt and topographic relief have been removed. An orthophotograph has consistent scale
throughout and can be used as a map. |
| P |
| Photogrammetry: The science or art of obtaining reliable measurements by
photography. For GIS applications, aerial photogrammetry often provides the foundation to
develop base maps. |
| Pixel: One picture element. Often used synonymously with a raster or grid cell.
The smallest discrete element which makes up an image. |
| Planimetric: In mapping, refers to spatial data that do not include topographic
or relief data. |
| Point: A single x,y coordinate that represents a geographic feature too small
to be displayed as a line or area; for example, the location of a mountain peak or a
building location on a small-scale map. |
| Polygon: A coverage used to represent areas. A polygon is defined by the arcs
that make up its boundary. Polygons have attributes that describe the geographic feature
they represent. |
| Precision: Refers to the number of significant digits used to store numbers,
and in particular, coordinate values. Precision is important for accurate feature
representation, analysis and mapping. |
| Prime Meridian: The initial meridian or longitude 0 degree (Greenwich
Meridian), which creates the plane from which an angle is measured to establish the
longitude of a point (see Longitude). |
| Projection: A mathematical model that transforms the locations of features on
the earth's surface onto a 2-dimensional map surface. |
| Q |
| Query or Database Query: The retrieval and display of data from a database
about one or more features, such as a parcel, its size, owner, value and location or
address. |
| R |
| Raster Data: One method of storing, representing or displaying spatial data in
digital form. It consists of using cell data (not necessarily square) arranged in a
regular grid pattern in which each unit (pixel or cell) within the grid is assigned an
identifying value based on its characteristics (see Vector). |
| Record: In an attribute table this would consist of a single "row" of
descriptors for one feature in contrast to an item or field or column which consists of a
single attribute descriptor. |
| Relational Database: A database structure composed of more than one flat file
(2-dimensional arrays) that can be transformed to form new combinations because of
relations between the data in the records, in contrast to hierarchical and network
database structures. |
| Relative Map Accuracy: The accuracy of map elements in relation to a local
survey network that is not tied to the earth's geoid. The positions are accurate only
within a certain geographic area covered by the local survey network (see Absolute Map
Accuracy). |
| Resolution: A measure of the accuracy or detail of a graphic display expressed
as dots per inch, pixels per line, line per millimeter, etc. |
| S |
| Satellite Imagery: Digital data obtained from sensors carried in satellites. It
includes collecting data both in the visible and non-visible portions of the
electromagnetic spectrum. One system is the multispectral scanner carried in Landsat
satellites. |
| Slope: A measure of change in surface value over distance, expressed in degrees
or as a percentage. For example, a rise of 2 meters over a distance of 100 meters
describes a 2% slope with an angle of 1.15. Mathematically, slope is referred to as the
first derivative of the surface. |
| Spatial: Refers to features or phenomena distributed in space and, thus, having
physical, measurable dimensions. |
| T |
| Thematic Map: A map that displays the spatial distribution of a single
attribute or a specific topic, such as property assessments, soil types, or crime
locations. |
| Topography: The relief, elevation or shape of the earth in a given area. |
| Topology: The explicit definition of how map features represented by points,
lines and areas are related. Specifically, issues of connectivity and adjacency of
features are accounted for. |
| V |
| Vector Data: One method of storing, representing or displaying spatial data in
digital form. It consists of using coordinate pairs (x,y) to represent locations on the
earth. Features can take the form of single points, lines, arcs or closed lines (polygons)
(see Raster Data). |
| Vertex: One of a set of ordered x,y coordinates that constitutes a line. |
References:
The New Hampshire Geographically Referenced Analysis and Information Transfer System
(1999) GRANIT Net Glossary
http://www.granit.sr.unh.edu/cgi-bin/load_file?PATH=/about/gloss.htmlESRI (2003)
Glossary of GIS Terms http://www.esri.com/library/glossary/glossary.html
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