Original User: DeSchlong

We all know that simple polylines, when digitized, are given a DIRECTION. This is why the function "Flip Lines" exists in ArcToolbox. However, I would like to

The purpose of this is to add line decorations which need to point a certain way - in this case I have depression contours symbolized with tick marks that need to point inward but the direction of the tick marks is dependent on the direction the line was digitized originally.

We all know that simple polylines, when digitized, are given a DIRECTION. This is why the function "Flip Lines" exists in ArcToolbox. However, I would like to

**select all the lines of a certain direction**(left to right, or Clockwise/Counter-Clockwise, for example, or however they are described), and FLIP only these lines. How do I do this?The purpose of this is to add line decorations which need to point a certain way - in this case I have depression contours symbolized with tick marks that need to point inward but the direction of the tick marks is dependent on the direction the line was digitized originally.

Hi everyone. There is really no ready-made answer for this problem, so I worked through it myself.

To first understand the nature of the problem, read and understand this discussion on determining the direction (CW/CCW) of a vector (this is the key to the whole exercise). Practice some sample calculations in Excel to verify for yourself that it works. Now that you've got the calculus under your belt, the remaining tasks in ArcGIS are tedious but fairly trivial.

I've built a 2-step model to determine the line direction as above then flip those going the wrong way. It might be possible to package it into a tool some day but until then if you want to see what I did you should just send me a message.

Good luck! :cool: