design principles - What are the differences between vector graphics and raster graphics?

I understand from prior knowledge that there are two different image format / composition options available for creating images; raster and vector.

I would like to understand more about them, such as what the defining characteristics of each are, and what typical, generic use-cases each might have.

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1. 
   

   What are raster graphics composed of?

   
   
   
   
   • When would I want to choose raster over vector?
   
   
   
   

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2. 
   

   What are vector graphics composed of?

   
   
   
   
   • When would I want to choose vector over raster?
   
   
   
   

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Answer

Vector graphics are graphics in which the image is represented in a mathematical fashion. What this allows one to do is to zoom in an image to infinite precision. They are ideal for situations in which an image might be used at various resolutions and dimensions.

Raster graphics are of a fixed dimension, somewhat like a grid pattern with specified values at each point. These graphics are the default for things from the real world (IE, scanned images, photographs, etc). They are ideal for use when an image will only be used once, and will never need to be enlarged, or if portions are coming from a photograph or other real-world image.