|the Art of Making Maps,
the Science of Where You Are
The definitions on this page describe how the words are used in the
Many of the definitions overlap: "photograph" overlaps with "image"
and "image" overlaps with "map."
A camera is a device used to focus light onto a surface which is
sensitive to light.
If it is a film camera, the developed film can be processed into a
Electronic cameras (CCD cameras) measure the amount of light in a small
region (a pixel) and record the information.
If you transfer this information into a computer, you can display
An image is a visual presentation of information.
In the Cartography series, we usually mean images generated by a
The information can come from a calculation or from a measurement.
A map is a drawing or image which shows information as it
relates to position, or how something changes with position.
A road map shows the position of roads.
A topographic map shows how the height of land changes as you change
The word "pixel" comes from "picture element."
The "pix" is from "picture" and "el" is from "element."
Images on a computer are made up of tiny rectangular color
Computer monitors are often described by the number of pixels
they can display.
A photograph is the result of exposing a sensitive surface to light.
This includes photographs taken by a standard camera as well as
Usually, but not always, "photograph" refers to visible light: the
photograph is what you could expect to see with your own eyes, if
you were there.
In the Cartography series, the Apollo 11 view of Earth is a
photograph from a good 35 mm camera.
The aerial photograph of Bellevue in "Maps of the Seattle Area"
is taken with a special camera.
A sensor is simply a device to measure something, often something
that humans can't see or feel themselves.
This series presents images from Landsat and AVHRR satellites.
These satellites use sensor systems to measure the amount of light
that is reflected or given off by the Earth.
The measurements are beamed to Earth by radio and computers turn
the numbers into images.
Hugh Anderson, and
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Fri Jan 24 23:22:18 1997