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Discrete data - ✔✔Represents real-world features that have well defined boundaries. A
discrete feature is distinct from the other features around it.
Example: A river is a discrete feature: there is a distinct place where you stop being dry
and begin getting wet.
Continuous data - ✔✔Represents real-world features that do not have well-defined
boundaries.
Examples: Elevation, temperature, rainfall.
There are no distinct places where the phenomena simply stop; values may change
abruptly, but the phenomena continue to be measured.
Hint: if it makes sense to take an average of the values, it is likely continuous data
Geographic Coordinate System (GCS) - ✔✔Uses a spherical model to identify points or
areas on the surface of the earth. Each coordinate system is commonly illustrated with a
network of intersecting lines of latitude and longitude called a graticule
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, Graticule - ✔✔a network of intersecting lines representing meridians (longitude) and
parallels (latitude), on which a map or plan can be represented
Four components of a coordinate system - ✔✔Angular units of measure
Prime meridian: Zero value for longitude
Spheroid: Mathematical model that estimates the size and shape of the Earth
Datum: A frame of reference for measuring locations on the surface of the Earth. It
defines the origin and orientation of latitude and longitude lines.
Why are there multiple spheroids in use for geographic coordinate systems? - ✔✔The
Earth's surface is not symmetrical, causing the semi major and semi minor axes that
work for one geographic region to not work for another region
Projected coordinate system - ✔✔A system that defines locations on a flat map based on
x,y coordinates
Projection types - ✔✔cylindrical, conic, azimuthal (planar)
Cylindrical projection - ✔✔a map created by projecting Earth's image onto a cylinder.
Meridians and parallels intersect at right angles, as they do on the globe
Conic projection - ✔✔Created by setting a cone over a globe and projecting light from
the center of the globe onto the cone. In general, distortion increases north and south of
the standard parallel
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