Altitude
The height of an object. In astronomy, altitudes are often
measured as the angular distance above the horizon.
Angle of insolation
The angle at which the sun's rays strike a surface, or the measured
altitude of the Sun above the horizon.
Circumference
The distance around a circle or a sphere.
Contour interval
The difference in elevation between adjacent contour lines.
Contour line
A line on a topographic map (contour map) that follows the contours
of the land by connecting points having the same elevation. An isoline for
elevation.
Contour map
Also called topographic map; a map that uses isolines to represnt the
topography of an area.
Cross section
A graph, profile or side view that represents a feature or structure.
Diameter
The distance across a circle that passes through the center of the circle.
Distance
The separation in time or space between two points or locations.
Elevation
The vertical distance (height) of a surface above an accepted reference
point, usually sea level. Elevation generally measures the height of a
surface where as altitude indicates the height of an object above a surface.
Equator
An imaginary line drawn around the Earth midway between the North and
South Poles. The basic reference point for the system of latitude.
Equatorial diameter
The distance through the center of a sphere whose plane contains the
equator of the sphere. The equatorial diameter of the Earth is 12,756 km.
Field
A region of space in which there is a measurable value for some quantity at
every point. Fields are represented in two dimensions as field diagrams or maps.
Weather maps, topographic maps, and geologic maps are all examples of fields.
Field quantity
The measurement or value that define a field.
Gradient
The slope or rate of change on a graph or field diagram. The closer the
isolines on a map, the steeper the gradient.
Hachure contour lines
Contour lines that are used to indicate a depression. The lines are shaded
(hatchured) to indicate the down-slope depression.
Horizon
The interface where the atmosphere appears to meet the surface of the
Earth. The apparent altitude of many celestial objects can be described as an angle
above an observer's horizon.
Isoline
Iso-intensity line. A line drawn on a field map that connects points having
the same value.
Isotherm
Line connecting points of equal temperature on a field diagram, such as a
weather map.
Landscape region
A physiographic province. A region with similar bedrock type and
structure, and climate.
Latitude
The angular distance (in degrees) measured North and South of the equator.
The latitude of an observer is equal to the altitude of Polaris.
Longitude
The angular distance, measured in degrees, east and west of the Prime
Meridian.
Magnetic field
The region of magnetic force that surrounds the Earth. Movement of molten iron in
the Earth's outer core is believed to create this physical force that extends into space.
Map
A model or representation of some field quantity shown in two dimensions.
Field diagrams of weather, pollution, elevation, and bedrock are very important in
the Earth Sciences.
Map profile
A side view or cross-sectional view of a selected portion of a map.
Maximum elevation
The greatest possible height on a section of a topographic map. The
maximum elevation is calculated by adding one less than the contour interval to the
highest elevation indicated by a contour line.
Minimum elevation
The lowest elevation indicated on a topographic map. To find the minimum
elevation of a point or an area, if it is not on a contour line, subtract one less than
the contour interval from the value indicated by the lowest contour line.
Model
A representation or working hypothesis of an object or phenomenon that
cannot be observed directly or is difficult to observe directly.
North Pole
Geographic North. The point on the Earth's located where the axis of
rotation intersects the surface.
Northern Hemisphere
The half of the Earth located between the equator and the North Pole.
Oblate sphere
A sphere that is slightly flattened on the top and bulges on its sides. A
celestial object becomes oblate as it rotates on its axis.
Parallels
Lines of latitude. Parallels of latitude are equidistant.
Polar diameter
The distance through the center of a sphere that connects the two poles. The
polar circumference of the Earth equals 12,714 km.
Polar Map Projection
A form of map in which a pole is located as the central point; the equator
forms the outer circle, and meridians of longitude are indicated by radii.
Polaris
The North Star, or the star that appears to be located above the Earth's North
Pole.
Prime Meridian
The 0° meridian. The imaginary line that extends from the North Pole to the
South Pole and passes through Greenwich, England. The reference point for Earth's
system of longitude.
Profile
A graph that represents the change in the field quantity vs. distance. A side
view of an object.
Relief
The shape of the surface in an area as indicated by differences of height and
steepness of slope. In general, relief can be calculated by measuring the difference
between the tops of the highest elevations to the bottom of their valleys. Mountains
and plateaus generally have high relief - measured in thousands of feet. Plains have
low relief which is measured in hundreds of feet.
Rotation
The spinning of an object on its axis. The rotation of the Earth once every
24 hours causes the Coriolis effect and the apparent change in the path of a Foucault
pendulum.
Slope
Gradient or rate of change. The amount of change that occurs per unit
distance. The amount of incline of a line or surface.
Solar noon
The time of day when the Sun reaches its maximum daily altitude, is due
south, or is on an observer's meridian.
Solar time (apparent solar time)
A system of measuring time that is based on the apparent motions of the
Sun. The length of day measured using the Sun as a reference varies from the length
of day using stars as a reference.
Time zone
One of the twenty four regions into which time on Earth is divided. Each
time zone is determined by 15° of rotation and changes one hour.
Topographic map
A map that shows the relief of the land surface through the use of contour
lines.
Topography
A description of the shape of the land surface. The hills, valleys, and slopes
that make up the surface of a region.
Zenith
The point in the sky located directly above an observer.