Glossary
A-D | E-F | G | H-I | L-M | N-P | Q-S | T
Quadrangle (quad) maps
A rectangular, or nearly rectangular, area covered by a map. The outline
is generally defined by latitude or longitude. Typically refers to
USGS topographic maps or to a map sheet published by the U.S. Geological
Survey. Also known as a topographic or topo map.
Raster data
One of the three types of spatial data in a GIS (the others being
image and vector data). Raster data represents geographic space as
a matrix of cells; map features are defined by numeric values assigned
to the cells. Cell data are arranged in a regular grid pattern in
which each unit (or cell) in the grid is assigned an identifying value
based on its characteristics. Information obtained from image sources
such as remote sensing from photography and satellite. Raster data
thus refers to data in the form of parallel scan-line segments, grid
cells or pixels. Also known as Cell System or Grid System.
Remote sensing
The act of detection, acquisition and recording, identification and
interpretation, or analysis of geographic imagery or data and information
about the properties of objects or conditions or phenomenon using
a sensing and recording device from a distance without having the
sensor in direct physical contact with the object of the study. Typically,
data and information is gathered using remote sensing methods, which
might be hand-held, airborne, or by satellite sensor. It includes
photography, aerial photography or satellite imagery, radar, and satellite
imaging extended from points in space. Satellites with sensors sensitive
to various bands of the electromagnetic spectrum provide a remote
sensing platform for LANDSAT analysis of elements as, e.g., land use,
geology and soils data. Remote sensing is a discipline that evolved
from photogrammetry to remote sensing of the Earth's resources using
aerial or space photographs, electronic scanners and sensors, and
other devices to collect data about the Earth's surface or subsurface
at a substantial distance from the targeted area.
Resolution (spatial)
A measure of the accuracy or detail of a graphic display, expressed
as dots per inch, pixels per line, lines per millimeter, etc. It is
a measure of how fine an image is, usually expressed in dots per inch
(dpi). The minimum difference or distance between two independently
measured or computed values or objects that can be distinguished by
the measurement or analytical method, or sensor being considered or
used. It provides a limit to precision and accuracy. Often called
spatial resolution but also applies to spectral and temporal aspects
of remote sensing imaging systems.
Resolution is the accuracy at which a given map scale can depict the location and shape of map features; the larger the map scale, the higher the possible resolution. As map scale decreases, resolution diminishes and feature boundaries must be smoothed, simplified, or not shown at all. It is the size of the smallest feature that can be represented in a surface. For example, small areas may have to be represented as points.
Route analysis
A method of determining the minimum distance between points to determine
efficiency of pedestrian and vehicle paths, travel times of routes,
and most effective routes and means of linear distribution. Used for
emergency vehicle dispatch, routing of buses and maintenance vehicles.
The data representing several variables is analyzed to produce an
optimum location for a route. Utilizing a digitized network, line
segments and nodes are chained together to determine the minimum distance
between point A and point B and thus measure the efficiency of vehicle
(or other phenomena) paths.
Scientific/environmental data needs
Natural resource-oriented users will find that up-to-date satellite
imagery, aerial photographs, as well as topographic, climatic and
hydrographic data are all useful in environmental planning and resource
monitoring. The increasing concern with the environment makes the
environmental hazards data such as toxic material locations especially
useful. Scientific/environmental tasks include agricultural planning,
environmental hazard analysis, environmental impact assessment, environmental
monitoring, fire control and modeling, geological surveying, hazardous
material inventory, land use planning, resource inventory, timber
harvest planning, water runoff calculations, wetlands inventory, wildlife
habitat analysis.
Spatial analysis
Analytical techniques to determine the spatial distribution of a variable,
the relationship between the spatial distribution of variables, and
the association of the variables of an area. Spatial analysis is often
referred to as modeling. It refers to the analysis of phenomena distributed
in space and having physical dimensions (the location of, proximity
to, or orientation of objects with respect to one another; relating
to an area of a map as in spatial information and spatial analysis;
referenced or relating to a specific location on the Earth's surface).
Spatial analysis is the process of extracting or creating new information about a set of geographic features to perform routine examination, assessment, evaluation, analysis or modeling of data in a geographic area based on pre-established and computerized criteria and standards. Spatial analysis is a process of modeling, examining, and interpreting model results useful for evaluating suitability and capability, for estimating and predicting, and for interpreting and understanding.
In GIS, there are four traditional types of spatial analysis: spatial overlay and contiguity analysis, surface analysis, linear analysis, and raster analysis. It includes such GIS functions as topological overlay, buffer generation, and spatial or network modeling. Abbreviated SA.
Spatial data
Consists of information about the relationships of entities in space,
facts about the real world organized geographically, the location,
shape of, and relationships among geographic features, which are usually
stored as coordinates and topology. This is in contrast with spatially
referenced data which are thematic or applied data (such as addresses
coded by distribution routes planned by street address). Discrete
symbols (numbers, letters, or special characters) used to describe
some entities are organized according to the location of that entity
in the three-dimensional world.
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