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I have a shapefile containing around a hundred points (lat/longs). And, I have a shapefile that contains a polyline representing a river. The river is somewhat horizontal (runs east to west) but meanders quite a bit. I am trying to compute how far a point lies to the north or south of the river in meters.

So far I have used the ArcGIS Near tool. My understanding of this tool is that it computes the shortest/perpendicular distance from the closest part of the near feature (in my case the river/polyline). Since the river is not perfectly horizontal, these distances will contain a horizontal component.

How should I compute how far a point lies north or south from the river (i.e. no horizontal component and only vertical distance from the nearest point on the river)?

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If I've understood your question correctly, you should be able to use the Near tool to accomplish this.

  • You'll want to add fields that contain the X and Y coordinates of the points to that layer (Add XY Coordinates).
  • Run your Near, but set the Location option to LOCATION. This will add additional fields for NEAR_X and NEAR_Y.
  • Join (or Join Field) your original point layer to the near results
  • After you've done that you can just find the distance from NEAR_Y to POINT_Y.

This will give you the distance to the same point that's perpendicular to the river, but only along the Y axis.

If you wish find the distance only when that perpendicular line is vertical, which may not actually be the nearest:

  • Thanks. It is also the case that when using Near tool set to GEODESIC, I am computing distances in meters. Is there a way to compute the distances in degrees? – user52932 Sep 17 '15 at 19:56
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    @Evil Genius what happens if there is no angle = 0? – FelixIP Sep 17 '15 at 19:59
  • Possibly by "clearing" the coordinate systems from both shapefiles so that the units are "unknown." They would have to be latitude/longitude (using a geographic coordinate system) already. But why? Degrees are an angular measurement, not linear. – mkennedy Sep 17 '15 at 20:09
  • @mkennedy So I am trying to recreate an analysis done by someone else. What they did was that they simply use the near tool to compute GEODESIC distances in meters b/w the points and the river (The distances can be oblique to the river). Then they divide the distance by 111000 meter /degree conversion to put everything in degree distances. The resulting distances are used in some regression analysis. I have a feeling that using this constant conversion is incorrect. – user52932 Sep 17 '15 at 20:42
  • The length of a "degree" north-south does change slowly between the equator and the pole. It's much less than the change in the east-west direction. The max is around 20 m per change of degree near 45N or S. – mkennedy Sep 17 '15 at 20:46
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If you use the linear referencing toolbox (tool named "Locate Features Along Routes" after having used "Create Routes" on your river), you could create a point at the place where the distance is shorter. Than you could compute any horizontal or vertical distance based on the coordinates (Y of source point minus Y of river line projected point)

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