1

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)?

Improve this question
1

2 Answers 2

Reset to default
1

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:

Improve this answer
12
  • 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, 2015 at 19:56
  • 1
    @Evil Genius what happens if there is no angle = 0?
    – FelixIP
    Sep 17, 2015 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, 2015 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, 2015 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, 2015 at 20:46
1

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)

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.