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Why do contour lines on a topo map never cross each other?

Each line is one exact elevation, and one spot cannot be two heights.

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  1. One spot can't sit at two elevations at once ✔
  2. Mapmakers erase the crossings to keep maps neat
  3. They do cross wherever two trails meet

Why: A contour line marks one exact height. If two lines crossed, the crossing point would have two different elevations at once, which is impossible.

Huh, didn't know that: Narrower intermediate contours between the wide index contours fill in the shape of the land.

The dad joke
Two contour lines met at a party. They kept their distance.
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References

Answer: One spot can't sit at two elevations at once. A contour line marks one exact height. If two lines crossed, the crossing point would have two different elevations at once, which is impossible.

  1. USGS: Topographic Map Symbols pubs.usgs.gov/gip/TopographicMapSymbols/topomapsymbols.pdf
    Each contour is a line of equal elevation; therefore, contours never cross.
    Checked 2026-10-08.

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Outdoors & CampingOn a topographic map, what does a contour line connect?Outdoors & CampingContour lines on your map are packed very close together. What does that mean?Outdoors & CampingWhy might the declination printed on an old topo map be wrong today?

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