I've been using the term Sea Level Distance to describe the total length of a line string where I ignore the elevation and just calculate the distance from point to point along the ellipsoid and sum the total.

Sea Level Distance has always seemed to be an artificial term for this. Slope Distance seems to naturally describe the distance when elevation is included. Is there a term for Sea Level Distance that is more natural and usable for novice users.

  • One old fashioned term that works perfectly, and sums what you require up, without needing to introduce a new lexicon, is 'as the crow flies'. Unless I have mistaken the question.
    – Hairy
    Commented Nov 25, 2011 at 13:47
  • Thanks for the answer. as the crow flies won't work because that implies a straight line from start to finish. Trails are never that straight!
    – Sarge
    Commented Dec 5, 2011 at 13:58

3 Answers 3


Geographic distance can be described in a number of ways, depending on the surface abstraction used:

  • For flat surface models, Euclidean distance is appropriate.

  • For spherical surface models, you would probably use great-circle distance.

  • For ellipsoidal surface models geodesic distance may be more appropriate, as the shortest distance between two points on an ellipsoid is not exactly the same as the great circle distance.

  • Thanks. I'm calculating using Vincenty's formula so Euclidean and great-circle are out. The terms geographic, geodesic and ellipsoidal would be scary to users and I don't feel they clearly show that elevation is not included.
    – Sarge
    Commented Nov 24, 2011 at 5:35
  • How about "globe distance", i.e. the distance you would get if you were to measure a piece of string laid on a smooth globe?
    – blah238
    Commented Nov 24, 2011 at 9:00

What about "2D distance"? That's a term i've used as opposed to 3D distance (your slope distance)

  • Good suggestion, I think as always it depends on the context and audience whether more or less technical terms are more suitable. I would equate 2D distance with Euclidean distance and would suggested it is only technically applicable with projected coordinates in Euclidean space.
    – blah238
    Commented Apr 23, 2012 at 23:02

How about just using 'distance'? Not sure what your application is, but most people would assume distance relates to the length of the path from one point to another following a given route. Mind you, I'm from a flat part of the world and maybe it's different where you are.

  • I dunno about that, leaves too much to question :)
    – blah238
    Commented Apr 24, 2012 at 6:53

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