Technical Terms

The definitions on this page describe how the words are used in the Cartography series. Many of the definitions overlap: "photograph" overlaps with "image" and "image" overlaps with "map."

• camera
  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 photograph. 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.
• image
  An image is a visual presentation of information. In the Cartography series, we usually mean images generated by a computer. The information can come from a calculation or from a measurement.
• map
  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 position.
• pixel
  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 spots: pixels. Computer monitors are often described by the number of pixels they can display.
• photograph
  A photograph is the result of exposing a sensitive surface to light. This includes photographs taken by a standard camera as well as electronic cameras. 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.
• sensor
  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.

Related Information

• Cartography Table of Contents
• Cartography Web Sites
• Up to Geography: Observing and Representing the Earth

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