G-3
Glossary
CORS the Continuously Operating Reference
Stations—a system operated by the National Geodetic
Survey to provide a ground-based method of obtaining
more accurate GPS positioning.
coverage a data layer represented by a group of files
in a workspace consisting of a directory structure
filled with files and also associated files in an INFO
directory.
data classification various methods used for
grouping together (and displaying) values on a
choropleth map.
datum a reference surface of Earth.
datum transformation changing measurements
from one datum to measurements in another datum.
decimal degrees (DD) the fractional decimal
equivalent to coordinates found using degrees,
minutes, and seconds.
degrees, minutes, and seconds (DMS) the
measurement system used in GCS.
DEM Digital Elevation Model—a representation of
the terrain surface, created by measuring a set of
equally spaced elevation values.
DGPS differential GPS—a method using a groundbased correction in addition to the satellite signals in
position determination.
digitizing the creation of vector objects through
sketching or tracing representations from a map or
image source.
Dijkstra’s Algorithm an algorithm used in
calculating the shortest path between an origin node
and other destination nodes in a network.
discrete object view the conceptualization of the
world that all items can be represented with a series of
objects.
dissolve the ability of the GIS to combine polygons
with the same features together.
DLG a Digital Line Graph—the features (such as roads,
rivers, or boundaries) digitized from USGS maps.
DOQ a Digital Orthophoto Quad. Orthophotos that
cover an area of 3.75 minutes of latitude by 3.75
minutes of longitude, or one-fourth of a 7.5 minute
USGS quad.
DPI Dots Per Inch—a measure of how coarse (lower
values) or sharp (higher values) an image or map
resolution will be when exported to a graphical
format.
draping a process in which an image is given z-values
to match the heights in a digital terrain model.
DRG a Digital Raster Graphic—a scanned version of a
USGS topographic map.
DTM a representation of a terrain surface
calculated by measuring elevation values at a series
of locations.
dual frequency a GPS receiver that can pick up both
the L1 and L2 frequency.
Earth Observation Day a day dedicated to remote
sensing research and education.
easting a measurement of so many units east (or
west) of some principal meridian.
edge a term used for the linkages of a network.
EGNOS a Satellite Based Augmentation System that
covers Europe.
electromagnetic spectrum the light energy
wavelengths and the properties associated with them.
ellipsoid a model of the rounded shape of Earth.
EO-1 a satellite launched in 2000 and set to orbit 1
minute after Landsat 7.
EOS NASA’s Earth Observing System mission
program.
ephemeris data referring to the GPS satellite’s
position in orbit.
Equal Interval a data classification method that
selects class break levels by taking the total span of
values (from highest to lowest) and dividing by the
number of desired classes.
Equator the line of latitude that runs around the
center of Earth and serves as the 0 degree line to make
latitude measurements from.
EROS the Earth Resources Observation Science
Center; located outside Sioux Falls, South Dakota,
which serves (among many other things) as a
downlink station for satellite imagery.
Esri the Environmental Systems Research Institute, a
key developer and leader of Geographic Information
Systems products.
ETM+ the Enhanced Thematic Mapper sensor
onboard Landsat 7.
Exclusive Or the operation wherein the chosen
features are all of those that meet the first criteria
as well as all of those that meet the second criteria,
except for the features that have both criteria in
common in the query.
Glossary
CORS the Continuously Operating Reference
Stations—a system operated by the National Geodetic
Survey to provide a ground-based method of obtaining
more accurate GPS positioning.
coverage a data layer represented by a group of files
in a workspace consisting of a directory structure
filled with files and also associated files in an INFO
directory.
data classification various methods used for
grouping together (and displaying) values on a
choropleth map.
datum a reference surface of Earth.
datum transformation changing measurements
from one datum to measurements in another datum.
decimal degrees (DD) the fractional decimal
equivalent to coordinates found using degrees,
minutes, and seconds.
degrees, minutes, and seconds (DMS) the
measurement system used in GCS.
DEM Digital Elevation Model—a representation of
the terrain surface, created by measuring a set of
equally spaced elevation values.
DGPS differential GPS—a method using a groundbased correction in addition to the satellite signals in
position determination.
digitizing the creation of vector objects through
sketching or tracing representations from a map or
image source.
Dijkstra’s Algorithm an algorithm used in
calculating the shortest path between an origin node
and other destination nodes in a network.
discrete object view the conceptualization of the
world that all items can be represented with a series of
objects.
dissolve the ability of the GIS to combine polygons
with the same features together.
DLG a Digital Line Graph—the features (such as roads,
rivers, or boundaries) digitized from USGS maps.
DOQ a Digital Orthophoto Quad. Orthophotos that
cover an area of 3.75 minutes of latitude by 3.75
minutes of longitude, or one-fourth of a 7.5 minute
USGS quad.
DPI Dots Per Inch—a measure of how coarse (lower
values) or sharp (higher values) an image or map
resolution will be when exported to a graphical
format.
draping a process in which an image is given z-values
to match the heights in a digital terrain model.
DRG a Digital Raster Graphic—a scanned version of a
USGS topographic map.
DTM a representation of a terrain surface
calculated by measuring elevation values at a series
of locations.
dual frequency a GPS receiver that can pick up both
the L1 and L2 frequency.
Earth Observation Day a day dedicated to remote
sensing research and education.
easting a measurement of so many units east (or
west) of some principal meridian.
edge a term used for the linkages of a network.
EGNOS a Satellite Based Augmentation System that
covers Europe.
electromagnetic spectrum the light energy
wavelengths and the properties associated with them.
ellipsoid a model of the rounded shape of Earth.
EO-1 a satellite launched in 2000 and set to orbit 1
minute after Landsat 7.
EOS NASA’s Earth Observing System mission
program.
ephemeris data referring to the GPS satellite’s
position in orbit.
Equal Interval a data classification method that
selects class break levels by taking the total span of
values (from highest to lowest) and dividing by the
number of desired classes.
Equator the line of latitude that runs around the
center of Earth and serves as the 0 degree line to make
latitude measurements from.
EROS the Earth Resources Observation Science
Center; located outside Sioux Falls, South Dakota,
which serves (among many other things) as a
downlink station for satellite imagery.
Esri the Environmental Systems Research Institute, a
key developer and leader of Geographic Information
Systems products.
ETM+ the Enhanced Thematic Mapper sensor
onboard Landsat 7.
Exclusive Or the operation wherein the chosen
features are all of those that meet the first criteria
as well as all of those that meet the second criteria,
except for the features that have both criteria in
common in the query.