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Imaginary line
Mathematical curve which does not physically exist / From Wikipedia, the free encyclopedia
For the technical use in mathematics, see Imaginary line (mathematics).
In general, an imaginary line is usually any sort of geometric line (more generally, curves) that has only an abstract definition and does not physically exist. They are often used to properly identify places on a map.
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Some outside geography do exist. A centerline is a nautical term for a line down the center of a vessel lengthwise.